[PATCH 09/60] drm/bridge: Add connector-related bridge operations and data
Andrzej Hajda
a.hajda at samsung.com
Thu Jul 11 12:41:01 UTC 2019
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.
Regards
Andrzej
>
>>> + 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 :-)
> -Daniel
>
>>
>> Regards
>>
>> Andrzej
>>
>>
>>> +
>>> + /**
>>> + * @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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