[PATCH 09/60] drm/bridge: Add connector-related bridge operations and data
Andrzej Hajda
a.hajda at samsung.com
Thu Aug 29 16:48:42 UTC 2019
On 26.08.2019 18:27, Laurent Pinchart wrote:
> Hi Andrzej,
>
> On Thu, Aug 22, 2019 at 02:17:16PM +0200, Andrzej Hajda wrote:
>> On 20.08.2019 00:45, Laurent Pinchart wrote:
>>> On Mon, Aug 19, 2019 at 10:38:35AM +0200, Andrzej Hajda wrote:
>>>> On 14.08.2019 14:40, Daniel Vetter wrote:
>>>>> On Wed, Aug 14, 2019 at 01:04:03PM +0300, Laurent Pinchart wrote:
>>>>>> On Wed, Aug 14, 2019 at 08:23:12AM +0200, Andrzej Hajda wrote:
>>>>>>> On 11.08.2019 00:43, Laurent Pinchart wrote:
>>>>>>>> On Fri, Aug 09, 2019 at 01:55:53PM +0200, Andrzej Hajda wrote:
>>>>>>>>> On 08.08.2019 21:32, Laurent Pinchart wrote:
>>>>>>>>>> On Tue, Jul 16, 2019 at 03:57:21PM +0200, Andrzej Hajda wrote:
>>>>>>>>>>> On 16.07.2019 11:00, Daniel Vetter wrote:
>>>>>>>>>>>> On Fri, Jul 12, 2019 at 11:01:38AM +0200, Andrzej Hajda wrote:
>>>>>>>>>>>>> On 11.07.2019 17:50, Daniel Vetter wrote:
>>>>>>>>>>>>>> On Thu, Jul 11, 2019 at 05:12:26PM +0200, Andrzej Hajda wrote:
>>>>>>>>>>>>>>> On 11.07.2019 15:18, Daniel Vetter wrote:
>>>>>>>>>>>>>>>> On Thu, Jul 11, 2019 at 02:41:01PM +0200, Andrzej Hajda wrote:
>>>>>>>>>>>>>>>>> On 11.07.2019 09:35, Daniel Vetter wrote:
>>>>>>>>>>>>>>>>>> On Wed, Jul 10, 2019 at 02:12:14PM +0200, Andrzej Hajda wrote:
>>>>>>>>>>>>>>>>>>> Hi Laurent,
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> I like the approach, current practice when almost every bridge should
>>>>>>>>>>>>>>>>>>> optionally implement connector, or alternatively downstream bridge or
>>>>>>>>>>>>>>>>>>> panel is very painful.
>>>>>>>>>>>>>>>>>> Yeah I think this looks mostly reasonable. Some api design comments on top
>>>>>>>>>>>>>>>>>> of Andrzej', with the fair warning that I didn't bother to read up on how
>>>>>>>>>>>>>>>>>> it's all used in the end. I probably should go and do that, at least to
>>>>>>>>>>>>>>>>>> get a feeling for what your hpd_cb usually does.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> More comments inlined.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> On 07.07.2019 20:18, Laurent Pinchart wrote:
>>>>>>>>>>>>>>>>>>>> To support implementation of DRM connectors on top of DRM bridges
>>>>>>>>>>>>>>>>>>>> instead of by bridges, the drm_bridge needs to expose new operations and
>>>>>>>>>>>>>>>>>>>> data:
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> - Output detection, hot-plug notification, mode retrieval and EDID
>>>>>>>>>>>>>>>>>>>> retrieval operations
>>>>>>>>>>>>>>>>>>>> - Bitmask of supported operations
>>>>>>>>>>>>>>>>>>> Why do we need these bitmask at all? Why cannot we rely on presence of
>>>>>>>>>>>>>>>>>>> operation's callback?
>>>>>>>>>>>>>>>>>> Yeah also not a huge fan of these bitmasks. Smells like
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> DRIVER_GEM|DRIVER_MODESET, and I personally really hate those. Easy to
>>>>>>>>>>>>>>>>>> add, generally good excuse to not have to think through the design between
>>>>>>>>>>>>>>>>>> different parts of drivers - "just" add another flag.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> - Bridge output type
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Add and document these.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Three new bridge helper functions are also added to handle hot plug
>>>>>>>>>>>>>>>>>>>> notification in a way that is as transparent as possible for the
>>>>>>>>>>>>>>>>>>>> bridges.
>>>>>>>>>>>>>>>>>>> Documentation of new opses does not explain how it should cooperate with
>>>>>>>>>>>>>>>>>>> bridge chaining, I suppose they should be chained explicitly, am I
>>>>>>>>>>>>>>>>>>> right? More comments about it later.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>>>>>>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>>>>>> drivers/gpu/drm/drm_bridge.c | 92 +++++++++++++++++++
>>>>>>>>>>>>>>>>>>>> include/drm/drm_bridge.h | 170 ++++++++++++++++++++++++++++++++++-
>>>>>>>>>>>>>>>>>>>> 2 files changed, 261 insertions(+), 1 deletion(-)
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
>>>>>>>>>>>>>>>>>>>> index 519577f363e3..3c2a255df7af 100644
>>>>>>>>>>>>>>>>>>>> --- a/drivers/gpu/drm/drm_bridge.c
>>>>>>>>>>>>>>>>>>>> +++ b/drivers/gpu/drm/drm_bridge.c
>>>>>>>>>>>>>>>>>>>> @@ -70,6 +70,8 @@ static LIST_HEAD(bridge_list);
>>>>>>>>>>>>>>>>>>>> */
>>>>>>>>>>>>>>>>>>>> void drm_bridge_add(struct drm_bridge *bridge)
>>>>>>>>>>>>>>>>>>>> {
>>>>>>>>>>>>>>>>>>>> + mutex_init(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> mutex_lock(&bridge_lock);
>>>>>>>>>>>>>>>>>>>> list_add_tail(&bridge->list, &bridge_list);
>>>>>>>>>>>>>>>>>>>> mutex_unlock(&bridge_lock);
>>>>>>>>>>>>>>>>>>>> @@ -86,6 +88,8 @@ void drm_bridge_remove(struct drm_bridge *bridge)
>>>>>>>>>>>>>>>>>>>> mutex_lock(&bridge_lock);
>>>>>>>>>>>>>>>>>>>> list_del_init(&bridge->list);
>>>>>>>>>>>>>>>>>>>> mutex_unlock(&bridge_lock);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + mutex_destroy(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>>>>> EXPORT_SYMBOL(drm_bridge_remove);
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> @@ -463,6 +467,94 @@ void drm_atomic_bridge_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>>>>> EXPORT_SYMBOL(drm_atomic_bridge_enable);
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> +/**
>>>>>>>>>>>>>>>>>>>> + * drm_bridge_hpd_enable - enable hot plug detection for the bridge
>>>>>>>>>>>>>>>>>>>> + * @bridge: bridge control structure
>>>>>>>>>>>>>>>>>>>> + * @cb: hot-plug detection callback
>>>>>>>>>>>>>>>>>>>> + * @data: data to be passed to the hot-plug detection callback
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Call &drm_bridge_funcs.hpd_enable and register the given @cb and @data as
>>>>>>>>>>>>>>>>>>>> + * hot plug notification callback. From now on the @cb will be called with
>>>>>>>>>>>>>>>>>>>> + * @data when an output status change is detected by the bridge, until hot plug
>>>>>>>>>>>>>>>>>>>> + * notification gets disabled with drm_bridge_hpd_disable().
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
>>>>>>>>>>>>>>>>>>>> + * bridge->ops. This function shall not be called when the flag is not set.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Only one hot plug detection callback can be registered at a time, it is an
>>>>>>>>>>>>>>>>>>>> + * error to call this function when hot plug detection is already enabled for
>>>>>>>>>>>>>>>>>>>> + * the bridge.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>> To simplify architecture maybe would be better to enable hpd just on
>>>>>>>>>>>>>>>>>>> bridge attach:
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> bridge->hpd_cb = cb;
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> bridge->hpd_data = data;
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> ret = drm_bridge_attach(...);
>>>>>>>>>>>>>>>>>> Yeah I like this more. The other problem here is, what if you need more
>>>>>>>>>>>>>>>>>> than 1 callback registers on the same bridge hdp signal?
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> This way we could avoid adding new callbacks hpd_(enable|disable)
>>>>>>>>>>>>>>>>>>> without big sacrifices.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> One more thing: HPD in DisplayPort/HDMI beside signalling plug/unplug,
>>>>>>>>>>>>>>>>>>> notifies about sink status change, how it translates to this cb?
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> + void (*cb)(void *data,
>>>>>>>>>>>>>>>>>>>> + enum drm_connector_status status),
>>>>>>>>>>>>>>>>>>>> + void *data)
>>>>>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>>>>>> + if (!bridge || !bridge->funcs->hpd_enable)
>>>>>>>>>>>>>>>>>>>> + return;
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + mutex_lock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
>>>>>>>>>>>>>>>>>>>> + goto unlock;
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + bridge->hpd_cb = cb;
>>>>>>>>>>>>>>>>>>>> + bridge->hpd_data = data;
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + bridge->funcs->hpd_enable(bridge);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> +unlock:
>>>>>>>>>>>>>>>>>>>> + mutex_unlock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>>>>>>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> +/**
>>>>>>>>>>>>>>>>>>>> + * drm_bridge_hpd_disable - disable hot plug detection for the bridge
>>>>>>>>>>>>>>>>>>>> + * @bridge: bridge control structure
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Call &drm_bridge_funcs.hpd_disable and unregister the hot plug detection
>>>>>>>>>>>>>>>>>>>> + * callback previously registered with drm_bridge_hpd_enable(). Once this
>>>>>>>>>>>>>>>>>>>> + * function returns the callback will not be called by the bridge when an
>>>>>>>>>>>>>>>>>>>> + * output status change occurs.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
>>>>>>>>>>>>>>>>>>>> + * bridge->ops. This function shall not be called when the flag is not set.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> +void drm_bridge_hpd_disable(struct drm_bridge *bridge)
>>>>>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>>>>>> + if (!bridge || !bridge->funcs->hpd_disable)
>>>>>>>>>>>>>>>>>>>> + return;
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + mutex_lock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>>>>>> + bridge->funcs->hpd_disable(bridge);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + bridge->hpd_cb = NULL;
>>>>>>>>>>>>>>>>>>>> + bridge->hpd_data = NULL;
>>>>>>>>>>>>>>>>>>>> + mutex_unlock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>>>>>>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> +/**
>>>>>>>>>>>>>>>>>>>> + * drm_bridge_hpd_notify - notify hot plug detection events
>>>>>>>>>>>>>>>>>>>> + * @bridge: bridge control structure
>>>>>>>>>>>>>>>>>>>> + * @status: output connection status
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Bridge drivers shall call this function to report hot plug events when they
>>>>>>>>>>>>>>>>>>>> + * detect a change in the output status, when hot plug detection has been
>>>>>>>>>>>>>>>>>>>> + * enabled by the &drm_bridge_funcs.hpd_enable callback.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * This function shall be called in a context that can sleep.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> + enum drm_connector_status status)
>>>>>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>>>>>> + mutex_lock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>>>>>> + if (bridge->hpd_cb)
>>>>>>>>>>>>>>>>>>>> + bridge->hpd_cb(bridge->hpd_data, status);
>>>>>>>>>>>>>>>>>> So this isn't quite what I had in mind. Instead something like this:
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> /* iterates over all bridges in the chain containing @bridge */
>>>>>>>>>>>>>>>>>> for_each_bridge(tmp_bridge, bridge) {
>>>>>>>>>>>>>>>>>> if (tmp_bridge == bridge)
>>>>>>>>>>>>>>>>>> continue;
>>>>>>>>>>>>>>>>>> if (bridge->hpd_notify);
>>>>>>>>>>>>>>>>>> bridge->hpd_notify(tmp_bridge, bridge, status);
>>>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> encoder = encoder_for_bridge(bridge);
>>>>>>>>>>>>>>>>>> if (encoder->helper_private->bridge_hpd_notify)
>>>>>>>>>>>>>>>>>> encoder->helper_private->bridge_hpd_notify(encoder, bridge, status);
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> dev = bridge->dev
>>>>>>>>>>>>>>>>>> if (dev->mode_config.helper_private->bridge_hpd_notify)
>>>>>>>>>>>>>>>>>> dev->mode_config.helper_private->bridge_hpd_notify(dev, bridge, status)
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> No register callback needed, no locking needed, everyone gets exactly the
>>>>>>>>>>>>>>>>>> hpd they want/need.
>>>>>>>>>>>>>>>>> As I understand you want to notify every member of the pipeline.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> I think it should be enough to notify only the source, and then source
>>>>>>>>>>>>>>>>> should decide if/when the hpd should be propagated upstream.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> It looks more generic for me.
>>>>>>>>>>>>>>>> I'm not parsing ... do you think my idea is more generic and useful, or
>>>>>>>>>>>>>>>> the one from Laurent? Kinda confused here.
>>>>>>>>>>>>>>> Regarding general idea:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> 1. Laurent's approach is to notify only consumer, I guess usually video
>>>>>>>>>>>>>>> source.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> 2. Your is to notify all other bridges and encoder.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> And I prefer 1st approach, why:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> - the source can decide if/when and to who propagate the signal,
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> - is more generic, for example if bridge send signal to two
>>>>>>>>>>>>>>> monitors/panels, it can delay hpd propagation till both sinks are present,
>>>>>>>>>>>>>> With Laurent's approach the bridge cannot send the hpd to more than one
>>>>>>>>>>>>>> consumer. There's only 1 callback. So you're example doesn't work.
>>>>>>>>>>>>> If there will be two consumers, there will be two bridge attachments,
>>>>>>>>>>>>> thus there will be two notifications, it should work.
>>>>>>>>>>>> 2 consumers, 1 producer. There's only _one_ callback in the producer. The
>>>>>>>>>>>> callback is registered on the produce bridge, not on the consumer bridge
>>>>>>>>>>>> (or I'm totallly misreading what Laurent does here).
>>>>>>>>>>> I have assumed that if devices exposes two hardware sink interfaces it
>>>>>>>>>>> will expose two separate bridges - of course it will not work with
>>>>>>>>>>> "bridge chaining" thing, but this is a different story.
>>>>>>>>>> Daniel is right that the current implementation only allows one
>>>>>>>>>> consumer. This is however not a limitation of the API, but of its
>>>>>>>>>> implementation, as I only needed a single consumer. The helpers in this
>>>>>>>>>> series ensure that neither the consumer nor the producer poke in the
>>>>>>>>>> drm_bridge structure to call back to the HPD handler:
>>>>>>>>>>
>>>>>>>>>> - The consumer calls drm_bridge_hpd_enable() and
>>>>>>>>>> drm_bridge_hpd_disable(), which could offer a reference-counted
>>>>>>>>>> behaviour if desired without changes to the consumer.
>>>>>>>>>>
>>>>>>>>>> - The producer gets configured by .hpd_enable() and .hpd_disable(),
>>>>>>>>>> which could also easily accommodate reference-counting in the drm
>>>>>>>>>> bridge core without changes to the producer.
>>>>>>>>>>
>>>>>>>>>> - The producer notifies HPD with drm_bridge_hpd_notify(), which could
>>>>>>>>>> easily be extended to support multiple consumers without changes to
>>>>>>>>>> the producer.
>>>>>>>>>>
>>>>>>>>>> This is actually my second version of the HPD mechanism. The first
>>>>>>>>>> version was never posted, poked into drm_bridge, and required the
>>>>>>>>>> producer to be aware of the callbacks. After discussing this privately
>>>>>>>>>> with Daniel, I came up with the implementation in this series that,
>>>>>>>>>> while not supporting multiple consumers now, makes it easy to extend
>>>>>>>>>> later without minimal effort.
>>>>>>>>>>
>>>>>>>>>> Daniel's proposed implementation above looks reasonable to me, provided
>>>>>>>>>> we can iterate over the bridges in an order that don't depend on the
>>>>>>>>>> position of the producer in the chain (should be easy to solve by
>>>>>>>>>> starting at the encoder for instance). It however looks a bit like a
>>>>>>>>>> midlayer to me :-) That's why I have a similar implementation in the
>>>>>>>>>> connector-bridge helper, which could be extended to call
>>>>>>>>>> encoder->helper_private->bridge_hpd_notify() and
>>>>>>>>>> dev->mode_config.helper_private->bridge_hpd_notify() instead of
>>>>>>>>>> hardcoding drm_kms_helper_hotplug_event(). Moving the code to
>>>>>>>>>> drm_bridge_hpd_notify() would on the other hand set the notification
>>>>>>>>>> sequence towards the encoder and driver in stone. Daniel, do you think
>>>>>>>>>> that would be better ?
>>>>>>>>>>
>>>>>>>>>> I would like to remind everybody that this series isn't the last I will
>>>>>>>>>> ever submit, and I plan to do more work on drm_bridge and drm_panel. I'm
>>>>>>>>>> open to suggestions, and can address problems on top of these patches,
>>>>>>>>>> provided obviously that this series doesn't go in the wrong direction.
>>>>>>>>>> I'm of course also willing to rework this series, but given the amount
>>>>>>>>>> of work we have in the drm_bridge realm, I can't fix everything in one
>>>>>>>>>> go :-)
>>>>>>>>>>
>>>>>>>>>>>>>>> - it resembles hardware wires :)
>>>>>>>>>>>>>> This isn't for the hw wires afaiui. The hw hpd terminates in the source
>>>>>>>>>>>>>> bridge, which then calls drm_bridge_hpd_notify() to inform anyone else
>>>>>>>>>>>>>> interested in that hpd singal. This includes:
>>>>>>>>>>>>>> - Other bridges, e.g. if they provide CEC support.
>>>>>>>>>>>>>> - Other bridges, maybe they need to re-run the HDCP state engine
>>>>>>>>>>>>>> - Overall driver, so it can update the modes/connector status and send the
>>>>>>>>>>>>>> uevent to the driver.
>>>>>>>>>>>>>> - Overall display pipeline for this specific bridge, maybe you need to
>>>>>>>>>>>>>> shut down/re-enable the pipe because $reasons.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> That's at least my understanding from lots of chats with Laurent about
>>>>>>>>>>>>>> what he wants to do here.
>>>>>>>>>> That's correct, and that's what I was trying to implement :-) The
>>>>>>>>>> notification, in this patch series, goes from the producer bridge to a
>>>>>>>>>> central place (namely the connector, with a helper implementation
>>>>>>>>>> available as part of this series, but custom implementations in display
>>>>>>>>>> drivers are fine if needed) that then dispatches the notification to all
>>>>>>>>>> bridges (through the .lost_hotplug() operation, which we could replace
>>>>>>>>>> by an .hpd_notify() operation) for the first two purposes listed above,
>>>>>>>>>> and then to the overall driver. The only thing I don't support yet is
>>>>>>>>>> dispatching to the display pipeline (item 4 in the list above) as I had
>>>>>>>>>> no need for that, and didn't want to develop an API with no user. This
>>>>>>>>>> would however not be difficult to do when needed, the need is taken into
>>>>>>>>>> account in the proposed implementation.
>>>>>>>>>>
>>>>>>>>>>>>> I do not know the full picture, but the solution where particular bridge
>>>>>>>>>>>>> notifies everything unconditionally seems to me much less flexible.
>>>>>>>>>>>>>
>>>>>>>>>>>>> If HPD signals is received by the consumer, if there are no obstacles it
>>>>>>>>>>>>> can propagate it further, upstream bridge/encoder or to drm core - it
>>>>>>>>>>>>> will mimic your scenario.
>>>>>>>>>>>>>
>>>>>>>>>>>>> But there are also other scenarios where bridge does not want to
>>>>>>>>>>>>> propagate signal, because for example:
>>>>>>>>>>>>>
>>>>>>>>>>>>> - it wants to wait for other sinks to wake up,
>>>>>>>>>>>>>
>>>>>>>>>>>> The other sink can just do that in their hpd callback.
>>>>>>>>>>>>
>>>>>>>>>>>>> - it propagates HPD signal via hardware wire,
>>>>>>>>>>>> Again, the other sink can just not listen to sw hpd in that case, and use
>>>>>>>>>>>> the wire/hw hpd interrupt.
>>>>>>>>>>>>
>>>>>>>>>>> If it should ignore HPD, why it should receive it at all - it is
>>>>>>>>>>> unnecessary noise. And I am afraid with more complicated pipelines it
>>>>>>>>>>> will be impossible for particular component (bridge/encoder/whatever) to
>>>>>>>>>>> distinguish if HPD notification which came from non-directly connected
>>>>>>>>>>> component should be ignored or not.
>>>>>>>>>>>
>>>>>>>>>>>>> - first it wants to verify if the sink is valid/compatible/authorized
>>>>>>>>>>>>> device.
>>>>>>>>>>>> Now you lost me. Why would someone glue incompatible IP into a SoC or
>>>>>>>>>>>> board?
>>>>>>>>>>> Bridge can have external connectors, and the user can connect there
>>>>>>>>>>> anything.
>>>>>>>>>>>
>>>>>>>>>>>>> In general HPD is input signal for notify of state changes on particular
>>>>>>>>>>>>> bus, in case of typical video bridge on its output video bus.
>>>>>>>>>>>>>
>>>>>>>>>>>>> In case of bridges they have also input video buses, and they can send
>>>>>>>>>>>>> HPD signal via this bus, but this is indeed different HPD signal, even
>>>>>>>>>>>>> if for most cases they looks similar.
>>>>>>>>>>>> Ah, I think this is a problem we will eventually have. But it's not
>>>>>>>>>>>> something we're currently solving here at all I think.
>>>>>>>>>>> Currently sii8620 device in tm2 sends hpd signal upstream via hardware
>>>>>>>>>>> line, so this is not something from far future. And I guess with HPD
>>>>>>>>>>> broadcasting it could be racy/error prone, for example EDID reading can
>>>>>>>>>>> fail due to bridge being not ready (ddc of sii8620 is connected to i2c
>>>>>>>>>>> controller via hw wires also).
>>>>>>>>>>>
>>>>>>>>>>>>>>> And regarding implementation:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> 1. Laurent proposes to register callback drm_bridge_hpd_enable.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> 2. You propose to add ops hpd_notify in bridges and encoders.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Your proposition is more straightforward, but if we want to notify only
>>>>>>>>>>>>>>> source we should locate it by parsing notification chain (what about
>>>>>>>>>>>>>>> unchained bridges), or store pointer somewhere during attachment.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> It still leaves us with this ugly dualism - source is encoder or bridge,
>>>>>>>>>>>>>>> similarly to sink as bridge or panel, but fixing it can be done later.
>>>>>>>>>>>>>> Uh I think we're not talking about the same thing really. My understanding
>>>>>>>>>>>>>> is that this callback is if someone (outside of this bridge) is interested
>>>>>>>>>>>>>> in a hpd signal _from_ this bridge. Which means you can only ever have 1
>>>>>>>>>>>>>> listener.
>>>>>>>>>>>>> Do we have real life examples?
>>>>>>>>>>>>>
>>>>>>>>>>>>> I want to distinguish two situations:
>>>>>>>>>>>>>
>>>>>>>>>>>>> - another device wants to know if input bus of the bridge has changed state,
>>>>>>>>>>>>>
>>>>>>>>>>>>> - another device wants to know if output bus of the bridge has changed
>>>>>>>>>>>>> state.
>>>>>>>>>>>> Uh, that's what drm_bridge_state is for (if it ever happens). That's how
>>>>>>>>>>>> bridges can exchange state and information about each another. hpd is
>>>>>>>>>>>> about the physical world, i.e. "is there a cable plugged into the port
>>>>>>>>>>>> I'm driving?". We're not going to use fake hpd to update bridge state and
>>>>>>>>>>>> fun stuff like that, we have the atomic_check machinery for this.
>>>>>>>>>>> My question was if we have real examples that upstream device requires
>>>>>>>>>>> knowledge about state of output line of the bridge?
>>>>>>>>>>>
>>>>>>>>>>> To be more precise, we have following display pipeline:
>>>>>>>>>>>
>>>>>>>>>>> A-->B-->C
>>>>>>>>>>>
>>>>>>>>>>> And C sends HPD to B (ie signal that state of line between B and C
>>>>>>>>>>> changed). Does A really wants to know this information? or it should
>>>>>>>>>>> just need to know if state of line A-->B changed?
>>>>>>>>>> There's one real life example, where A is an HDMI encoder, B is an HDMI
>>>>>>>>>> ESD protector and level shifter, and C is the physical HDMI connector.
>>>>>>>>>> When the HDMI cable is unplugged, the CEC controller part of A needs to
>>>>>>>>>> be notified in order to reset the CEC state machine. One could however
>>>>>>>>>> argue that in that case the A-B link state changes too, but the
>>>>>>>>>> important part is that HPD detection is not performed by A, while A
>>>>>>>>>> needs to be informed of lost hotplug.
>>>>>>>>> I have no full picture but I guess in this case C sends HPD to B using
>>>>>>>>> hardware wire, and then B sends HPD to A also via wire, so I wouldn't
>>>>>>>>> say that B does not participate in HPD transmission/forwarding,
>>>>>>>> No, in this case A doesn't receive any hardware HPD signal, it requires
>>>>>>>> HPD notification through software.
>>>>>>>>
>>>>>>>>> some shifters with 'advanced power saving' can even perform wake-up of
>>>>>>>>> upstream pin logic after receiving HPD on downstream, so HPD sent from B
>>>>>>>>> to A is indeed different than HPD sent from C to B.
>>>>>>>>>
>>>>>>>>> Btw, with the above logic of propagation of HPD callback (proposed by
>>>>>>>>> Daniel) I guess it will work this way:
>>>>>>>>>
>>>>>>>>> - A will receive HPD signal via HW,
>>>>>>>>>
>>>>>>>>> - then B and C will receive HPD callback via framework.
>>>>>>>>>
>>>>>>>>> Am I right?
>>>>>>>> It's the other way around.
>>>>>>>>
>>>>>>>> In this case the HPD signal from the connector (C) is routed to an input
>>>>>>>> of the ESD chip (B). The ESD chip outputs a shifted HPD hardware signal
>>>>>>>> connected to a GPIO of the SoC. The driver for (B) thus registers a GPIO
>>>>>>>> IRQ and receive the hardware HPD notification. The driver for the HDMI
>>>>>>>> encoder (A) needs to receive HPD notification in software, through the
>>>>>>>> framework.
>>>>>>> If this is GPIO I wonder why do not query this gpio by encoder directly,
>>>>>>> rules of ownership of such gpios seems to be grey area, so in such case
>>>>>>> I would advise to put it in the driver who really needs it.
>>>>>>>
>>>>>>> This way it will be much simpler.
>>>>>> First to fall, multiple drivers may need to be informed of HPD events
>>>>>> coming from a GPIO, so we would need to duplicate it in multiple places,
>>>>>> and I don't think the GPIO framework allows acquiring a GPIO multiple
>>>>>> times.
>>>>>>
>>>>>> Then, the GPIO is described in DT, and DT doesn't care about which
>>>>>> driver needs HPD events. DT specifies the GPIO in the node of the device
>>>>>> it belongs to, this is defined in DT bindings, and must be the same on
>>>>>> all boards, while depending on the board different devices may need to
>>>>>> be informed of HPD events.
>>>>>>
>>>>>> For those two reasons HPD GPIO handling and consumption of HPD events
>>>>>> can't always be grouped in the same driver.
>>>>>>
>>>>>>> Going back to HPD notifications, as I said earlier broadcasting HPD
>>>>>>> notification unconditionally to every member of the chain with hope that
>>>>>>> the member will be able to filter-out undesired notification seems to me
>>>>>>> incorrect - maybe it can solve some problems but is not flexible enough
>>>>>>> to be usable in other scenarios.
>>>>>>>
>>>>>>> If my arguments do not convince you please just continue with your
>>>>>>> ideas, we can always add NO_HPD_BROADCAST somewhere :)
>>>>>> :-) I would like to understand the problems you're referring to though,
>>>>>> and hopefully solve them. If you could describe one of the scenarios
>>>>>> where you think this mechanism wouldn't be usable that would help. In
>>>>>> the meantime I will post a new version of the series with these
>>>>>> operations kept as-is to get the rest of the patches reviewed.
>>>>> See my little thing about midlayers, I think midlayers with lots of flags
>>>>> for everything aren't a good idea. They should be more opinionated about
>>>>> how things work.
>>>>>
>>>>> So if there's a case where this broadcasting of various things doesn't
>>>>> work, let's dig into it.
>>>>>
>>>> OK, almost real life example:
>>>>
>>>> A -> B -> C
>>>>
>>>> A - RGB/HDMI converter,
>>>>
>>>> B - HDMI/MHL converter,
>>>>
>>>> C - uUSB controller (MUIC).
>>>>
>>>>
>>>> C - detects presence of MHL sink and routes MHL lines to B in such case.
>>>>
>>>> B - has no hardware logic to detect HPD, but it's firmware can read EDID
>>>> from downstream component via HW lines and it has hardware lines to
>>>> upstream component to send EDID,
>>>>
>>>> A - can read EDID from B via hardware lines, but does not have hardware HPD.
>>> It probably doesn't matter much for the overall discussion, but out of
>>> curiosity, does B have a CBUS interface towards C and a DDC (I2C)
>>> interface towards A ?
>> Yes, but C (MUIC) is not MHL aware, beside initial 1K resistance
>> detection on ID pin, AFAIK.
>>
>>> And does A read the EDID on DDC and expose it
>>> towards the SoC through a custom protocol (for instance as the ADV7511
>>> does), or does it forward the DDC lines to the SoC ?
>>>
>>>> So how it should work (according to specification):
>>>>
>>>> 1. C detects MHL sink.
>>>>
>>>> 2. C switches his mux to route lines to B.
>>>>
>>>> 3. C sends HPD notification to B.
>>>>
>>>> 4. B powers on, its firmware reads EDID from downstream lines (possibly
>>>> adjusting it) and makes it available to upstream component A.
>>>>
>>>> 5. B sends HPD notification to A.
>>>>
>>>>
>>>> I do not know how it could work with HPD broadcasting.
>>>>
>>>> I guess C should be HPD provider, but in case of HPD broadcasting A and
>>>> B would receive notification in the same time, as a result A would start
>>>> reading EDID too early - fail.
>>> That's an interesting case indeed. Now I understand what you meant
>>> earlier.
>>>
>>> The HPD notification from C to B is purely internal, and should not be
>>> visible from a DRM/KMS point of view. It just happens that this hardware
>>> setup has a more complex HPD sequence that requires software
>>> intervention in the middle of the sequence. As such, if we forget about
>>> this patch series for a minute, C would need a custom API to send MHL
>>> notification to B, and the HPD for DRM/KMS would be notified by B, right
>>> ?
>> I just want to convince you that maybe all HPD signals
>> (hardware/software) are purely internal (ie they should be handled only
>> by upstream devices), and the hotplug event should be sent to
>> userspace/drm_core only when WHOLE pipeline is ready to query modes
>> (i2c/sideband channels/whatever is functional).
> I think that most HPD events are not internal, and that the above case
> is more an exception than a rule :-) It should however be supported, and
> I agree that HPD should be notified to the DRM core only when it has
> traversed the whole pipeline, yes.
>
> I'd like to keep bridge drivers simple though, and avoid requiring
> manual HPD propagation as I think that's the common case. That's why I
> proposed blocking the propagation below. What do you think ?
>
> This also means that, if we switch to a model where propagation can be
> disabled, a bridge will only notify upstream (closer to the CRTC)
> bridges. If, in a A-B-C chain, bridge B receives the external HPD event,
> then bridge C would never be notified. Do you think that could be an
> issue ?
As I said somewhere earlier it should work.
Btw, since bridges are currently connected via single-linked list (just
drm_bridge->next), do you plan to switch to double linked list, to find
upstream bridge, or add logic to discover upstream bridge on the fly?
>
>>> I think it's possible to handle both the MHL notification and the
>>> user-visible HPD notification through the same bridge API, provided that
>>> we offer a way for a bridge to block forwarding of the HPD notification.
>>> This will also require calling the HPD notifiers on bridges in the sink
>>> to source order. Both are doable, the bridge HPD notifier operation
>>> could return a bool that blocks propagation of the notification. Would
>>> that work for you ?
>> It could work, in this case.
>>
>> But it will still have problems with non-linear pipelines - where stream
>> is split to two or more bridges/panels.
> I agree, but that's not supported by the bridge API for now. I'm not
> sure I'm looking forward to dealing with this, but I think it will be
> needed :-)
Currently there are two modes of usage of bridge:
- part of bridge chain,
- private bridge - it can be attached to other components via private
pointer, not drm_encoder->bridge, nor drm_bridge->next.
Non-linear pipelines can be ( and I guess they are ) implemented using
the latter.
Anyway if we want to extend bridge API it would be good to allow usage
of this API also with detached bridges.
Regards
Andrzej
>
>>>>>>>>>>>>>> You seem to have some other idea here.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> + mutex_unlock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>>>>>>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> #ifdef CONFIG_OF
>>>>>>>>>>>>>>>>>>>> /**
>>>>>>>>>>>>>>>>>>>> * of_drm_find_bridge - find the bridge corresponding to the device node in
>>>>>>>>>>>>>>>>>>>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
>>>>>>>>>>>>>>>>>>>> index 08dc15f93ded..b9445aa5b1ef 100644
>>>>>>>>>>>>>>>>>>>> --- a/include/drm/drm_bridge.h
>>>>>>>>>>>>>>>>>>>> +++ b/include/drm/drm_bridge.h
>>>>>>>>>>>>>>>>>>>> @@ -23,8 +23,9 @@
>>>>>>>>>>>>>>>>>>>> #ifndef __DRM_BRIDGE_H__
>>>>>>>>>>>>>>>>>>>> #define __DRM_BRIDGE_H__
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> -#include <linux/list.h>
>>>>>>>>>>>>>>>>>>>> #include <linux/ctype.h>
>>>>>>>>>>>>>>>>>>>> +#include <linux/list.h>
>>>>>>>>>>>>>>>>>>>> +#include <linux/mutex.h>
>>>>>>>>>>>>>>>>>>>> #include <drm/drm_mode_object.h>
>>>>>>>>>>>>>>>>>>>> #include <drm/drm_modes.h>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> @@ -334,6 +335,110 @@ struct drm_bridge_funcs {
>>>>>>>>>>>>>>>>>>>> */
>>>>>>>>>>>>>>>>>>>> void (*atomic_post_disable)(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> struct drm_atomic_state *state);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @detect:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Check if anything is attached to the bridge output.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * This callback is optional, if not implemented the bridge will be
>>>>>>>>>>>>>>>>>>>> + * considered as always having a component attached to its output.
>>>>>>>>>>>>>>>>>>>> + * Bridges that implement this callback shall set the
>>>>>>>>>>>>>>>>>>>> + * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * RETURNS:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * drm_connector_status indicating the bridge output status.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + enum drm_connector_status (*detect)(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @get_modes:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Fill all modes currently valid for the sink into the &drm_connector
>>>>>>>>>>>>>>>>>>>> + * with drm_mode_probed_add().
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * The @get_modes callback is mostly intended to support non-probable
>>>>>>>>>>>>>>>>>>>> + * displays such as many fixed panels. Bridges that support reading
>>>>>>>>>>>>>>>>>>>> + * EDID shall leave @get_modes unimplemented and implement the
>>>>>>>>>>>>>>>>>>>> + * &drm_bridge_funcs->get_edid callback instead.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * This callback is optional. Bridges that implement it shall set the
>>>>>>>>>>>>>>>>>>>> + * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * RETURNS:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * The number of modes added by calling drm_mode_probed_add().
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + int (*get_modes)(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> + struct drm_connector *connector);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @get_edid:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Read and parse the EDID data of the connected display.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * The @get_edid callback is the preferred way of reporting mode
>>>>>>>>>>>>>>>>>>>> + * information for a display connected to the bridge output. Bridges
>>>>>>>>>>>>>>>>>>>> + * that support readind EDID shall implement this callback and leave
>>>>>>>>>>>>>>>>>>>> + * the @get_modes callback unimplemented.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * The caller of this operation shall first verify the output
>>>>>>>>>>>>>>>>>>>> + * connection status and refrain from reading EDID from a disconnected
>>>>>>>>>>>>>>>>>>>> + * output.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * This callback is optional. Bridges that implement it shall set the
>>>>>>>>>>>>>>>>>>>> + * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * RETURNS:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * An edid structure newly allocated with kmalloc() (or similar) on
>>>>>>>>>>>>>>>>>>>> + * success, or NULL otherwise. The caller is responsible for freeing
>>>>>>>>>>>>>>>>>>>> + * the returned edid structure with kfree().
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + struct edid *(*get_edid)(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> + struct drm_connector *connector);
>>>>>>>>>>>>>>>>>>> It overlaps with get_modes, I guess presence of one ops should disallow
>>>>>>>>>>>>>>>>>>> presence of another one?
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> I am not really convinced we need this op at all, cannot we just assign
>>>>>>>>>>>>>>>>>>> some helper function to .get_modes cb, which will do the same?
>>>>>>>>>>>>>>>>>> Plan B): ditch ->get_edid, require that the driver has ->get_modes in that
>>>>>>>>>>>>>>>>>> case, and require that if it has an edid it must fill out connector->info
>>>>>>>>>>>>>>>>>> and connector->edid correctly.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Btw if a hpd happens, who's responible for making sure the edid/mode list
>>>>>>>>>>>>>>>>>> in the connector is up-to-date? With your current callback design that's
>>>>>>>>>>>>>>>>>> up to the callback, which doesn't feel great. Maybe drm_bridge_hpd_notify
>>>>>>>>>>>>>>>>>> should guarantee that it'll first walk the connectors to update status and
>>>>>>>>>>>>>>>>>> edid/mode list for the final drm_connector. And then instead of just
>>>>>>>>>>>>>>>>>> passing the simple "status", it'll pass the connector, with everything
>>>>>>>>>>>>>>>>>> correctly updated.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Otherwise everyone interested in that hpd signal will go and re-fetch the
>>>>>>>>>>>>>>>>>> edid, which is not so awesome :-)
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @lost_hotplug:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Notify the bridge of display disconnection.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * This callback is optional, it may be implemented by bridges that
>>>>>>>>>>>>>>>>>>>> + * need to be notified of display disconnection for internal reasons.
>>>>>>>>>>>>>>>>>>>> + * One use case is to reset the internal state of CEC controllers for
>>>>>>>>>>>>>>>>>>>> + * HDMI bridges.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + void (*lost_hotplug)(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @hpd_enable:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Enable hot plug detection. From now on the bridge shall call
>>>>>>>>>>>>>>>>>>>> + * drm_bridge_hpd_notify() each time a change is detected in the output
>>>>>>>>>>>>>>>>>>>> + * connection status, until hot plug detection gets disabled with
>>>>>>>>>>>>>>>>>>>> + * @hpd_disable.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * This callback is optional and shall only be implemented by bridges
>>>>>>>>>>>>>>>>>>>> + * that support hot-plug notification without polling. Bridges that
>>>>>>>>>>>>>>>>>>>> + * implement it shall also implement the @hpd_disable callback and set
>>>>>>>>>>>>>>>>>>>> + * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + void (*hpd_enable)(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @hpd_disable:
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * Disable hot plug detection. Once this function returns the bridge
>>>>>>>>>>>>>>>>>>>> + * shall not call drm_bridge_hpd_notify() when a change in the output
>>>>>>>>>>>>>>>>>>>> + * connection status occurs.
>>>>>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>>>>>> + * This callback is optional and shall only be implemented by bridges
>>>>>>>>>>>>>>>>>>>> + * that support hot-plug notification without polling. Bridges that
>>>>>>>>>>>>>>>>>>>> + * implement it shall also implement the @hpd_enable callback and set
>>>>>>>>>>>>>>>>>>>> + * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + void (*hpd_disable)(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>>>>>> };
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> /**
>>>>>>>>>>>>>>>>>>>> @@ -372,6 +477,38 @@ struct drm_bridge_timings {
>>>>>>>>>>>>>>>>>>>> bool dual_link;
>>>>>>>>>>>>>>>>>>>> };
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> +/**
>>>>>>>>>>>>>>>>>>>> + * enum drm_bridge_ops - Bitmask of operations supported by the bridge
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> +enum drm_bridge_ops {
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
>>>>>>>>>>>>>>>>>>>> + * its output. Bridges that set this flag shall implement the
>>>>>>>>>>>>>>>>>>>> + * &drm_bridge_funcs->detect callback.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + DRM_BRIDGE_OP_DETECT = BIT(0),
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
>>>>>>>>>>>>>>>>>>>> + * connected to its output. Bridges that set this flag shall implement
>>>>>>>>>>>>>>>>>>>> + * the &drm_bridge_funcs->get_edid callback.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + DRM_BRIDGE_OP_EDID = BIT(1),
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
>>>>>>>>>>>>>>>>>>>> + * without requiring polling. Bridges that set this flag shall
>>>>>>>>>>>>>>>>>>>> + * implement the &drm_bridge_funcs->hpd_enable and
>>>>>>>>>>>>>>>>>>>> + * &drm_bridge_funcs->disable_hpd_cb callbacks.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + DRM_BRIDGE_OP_HPD = BIT(2),
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @DRM_BRIDGE_OP_MODES: The bridge can retrieving the modes supported
>>>>>>>>>>>>>>>>>>>> + * by the display at its output. This does not include readind EDID
>>>>>>>>>>>>>>>>>>>> + * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
>>>>>>>>>>>>>>>>>>>> + * this flag shall implement the &drm_bridge_funcs->get_modes callback.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + DRM_BRIDGE_OP_MODES = BIT(3),
>>>>>>>>>>>>>>>>>>>> +};
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> /**
>>>>>>>>>>>>>>>>>>>> * struct drm_bridge - central DRM bridge control structure
>>>>>>>>>>>>>>>>>>>> */
>>>>>>>>>>>>>>>>>>>> @@ -398,6 +535,29 @@ struct drm_bridge {
>>>>>>>>>>>>>>>>>>>> const struct drm_bridge_funcs *funcs;
>>>>>>>>>>>>>>>>>>>> /** @driver_private: pointer to the bridge driver's internal context */
>>>>>>>>>>>>>>>>>>>> void *driver_private;
>>>>>>>>>>>>>>>>>>>> + /** @ops: bitmask of operations supported by the bridge */
>>>>>>>>>>>>>>>>>>>> + enum drm_bridge_ops ops;
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @type: Type of the connection at the bridge output
>>>>>>>>>>>>>>>>>>>> + * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
>>>>>>>>>>>>>>>>>>>> + * identifies the type of connected display.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + int type;
>>>>>>>>>>>>>>>>>>>> + /** private: */
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + struct mutex hpd_mutex;
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @hpd_cb: Hot plug detection callback, registered with
>>>>>>>>>>>>>>>>>>>> + * drm_bridge_hpd_enable().
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + void (*hpd_cb)(void *data, enum drm_connector_status status);
>>>>>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>>>>>> + * @hpd_data: Private data passed to the Hot plug detection callback
>>>>>>>>>>>>>>>>>>>> + * @hpd_cb.
>>>>>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>>>>>> + void *hpd_data;
>>>>>>>>>>>>>>>>>>>> };
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> void drm_bridge_add(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>>>>>> @@ -428,6 +588,14 @@ void drm_atomic_bridge_pre_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> void drm_atomic_bridge_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> struct drm_atomic_state *state);
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> + void (*cb)(void *data,
>>>>>>>>>>>>>>>>>>>> + enum drm_connector_status status),
>>>>>>>>>>>>>>>>>>>> + void *data);
>>>>>>>>>>>>>>>>>>>> +void drm_bridge_hpd_disable(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>>>>>> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>>>>>> + enum drm_connector_status status);
>>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>> #ifdef CONFIG_DRM_PANEL_BRIDGE
>>>>>>>>>>>>>>>>>>>> struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel,
>>>>>>>>>>>>>>>>>>>> u32 connector_type);
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