[Intel-gfx] [PATCH v7 09/11] drm: uevent for connector status change

Ser, Simon simon.ser at intel.com
Tue May 14 06:18:48 UTC 2019 

On Mon, 2019-05-13 at 17:04 +0200, Daniel Vetter wrote:
> On Mon, May 13, 2019 at 10:11:01AM +0000, Ser, Simon wrote:
> > On Mon, 2019-05-13 at 11:34 +0200, Daniel Vetter wrote:
> > > On Mon, May 13, 2019 at 11:02 AM Paul Kocialkowski
> > > <paul.kocialkowski at bootlin.com> wrote:
> > > > Hi,
> > > > 
> > > > On Fri, 2019-05-10 at 16:54 +0200, Daniel Vetter wrote:
> > > > > On Fri, May 10, 2019 at 2:12 PM Paul Kocialkowski
> > > > > <paul.kocialkowski at bootlin.com> wrote:
> > > > > > Hi,
> > > > > > 
> > > > > > On Tue, 2019-05-07 at 21:57 +0530, Ramalingam C wrote:
> > > > > > > DRM API for generating uevent for a status changes of connector's
> > > > > > > property.
> > > > > > > 
> > > > > > > This uevent will have following details related to the status change:
> > > > > > > 
> > > > > > >   HOTPLUG=1, CONNECTOR=<connector_id> and PROPERTY=<property_id>
> > > > > > > 
> > > > > > > Need ACK from this uevent from userspace consumer.
> > > > > > 
> > > > > > So we just had some discussions over on IRC and at about the hotplug
> > > > > > issue and came up with similar ideas:
> > > > > > https://lists.freedesktop.org/archives/dri-devel/2019-May/217408.html
> > > > > > 
> > > > > > The conclusions of these discussions so far would be to have a more or
> > > > > > less fine grain of uevent reporting depending on what happened. The
> > > > > > point is that we need to cover different cases:
> > > > > > - one or more properties changed;
> > > > > > - the connector status changed;
> > > > > > - something else about the connector changed (e.g. EDID/modes)
> > > > > > 
> > > > > > For the first case, we can send out:
> > > > > > HOTPLUG=1
> > > > > > CONNECTOR=<id>
> > > > > > PROPERTY=<id>
> > > > > > 
> > > > > > and no reprobe is required.
> > > > > > 
> > > > > > For the second one, something like:
> > > > > > HOTPLUG=1
> > > > > > CONNECTOR=<id>
> > > > > > STATUS=Connected/Disconnected
> > > > > > 
> > > > > > and a connector probe is needed for connected, but not for
> > > > > > disconnected;
> > > > > > 
> > > > > > For the third one, we can only indicate the connector:
> > > > > > HOTPLUG=1
> > > > > > CONNECTOR=<id>
> > > > > > 
> > > > > > and a reprobe of the connector is always needed
> > > > > 
> > > > > There's no material difference between this one and the previous one.
> > > > > Plus there's no beenfit in supplying the actual value of the property,
> > > > > i.e. we can reuse the same PROPERTY=<id-of-status-property> trick.
> > > > 
> > > > That's the idea, but we need to handle status changes differently than
> > > > properties, since as far as I know, connected/unconnected status is not
> > > > exposed as a prop for the connector.
> > > 
> > > Oops, totally missed that. "Everything is a property" is kinda
> > > new-ish, at least compared to kms. Kinda tempted to just make status
> > > into a property. Or another excuse why we should expose the epoch
> > > property :-)
> > > 
> > > > > Here's why:
> > > > > - A side effect of forcing a probe on a connector is that you get to
> > > > > read all the properties, so supplying them is kinda pointless.
> > > > 
> > > > Agreed, except for the status case where it's useful to know it's a
> > > > disconnect, because we don't need any probe step in that case.
> > > > 
> > > > > - You can read STATUS without forcing a reprobe, if you want to avoid
> > > > > the reprobe for disconnected. I'd kinda not recommend that though,
> > > > > feels a bit like overoptimizing. And for reasonable connectors (i.e.
> > > > > dp) reprobing a disconnected output is fast. HDMI is ... less
> > > > > reasonable unfortunately, but oh well.
> > > > 
> > > > How would that be retreived then? From the looks of it, that's a
> > > > MODE_GETCONNECTOR ioctl and I was under the impression this is what
> > > > does the full reprobe.
> > > 
> > > drmGetConnector vs drmGetConnectorCurrent.
> > > 
> > > > Not sure what issues could arise in case of disconnect without reprobe
> > > > -- at least I don't see why userspace should have to do anything in
> > > > particular except no longer using the connector, even in complex DP MST
> > > > cases.
> > > 
> > > connector->status might be a lie without a full reprobe, and wrongly
> > > indicate that the connector is disconnected while there's still
> > > something plugged in. I'm not sure we've fixed those bugs by now
> > > (usually it's around "hpd indicates disconnected" vs. "i2c indicates
> > > connected, and we can't break this because every intel platform ever
> > > shipped has a few devices where this is somehow broken, irrespective
> > > of the sink).
> > > 
> > > > > - There's no way to only reprobe status, you can only ever reprobe
> > > > > everything with the current ioctl and implementations. Having an
> > > > > option to reprobe only parts of it doesn't seem useful to me (we need
> > > > > to read the EDID anyway, and that's the expensive part of reprobing in
> > > > > almost all cases).
> > > > 
> > > > Agreed.
> > > > 
> > > > > In a way PROPERTY=<status-prop-id> simply tells userspace that it
> > > > > needs to reprobe this connector.
> > > > 
> > > > I thought we could access the props alone, which avoids doing a reprobe
> > > > when the kernel knows that only a prop or a set of props changed and do
> > > > not require a full reprobe. That's the first case I was mentionning.
> > > > 
> > > > > At that point we need to figure out whether this is a good uapi or
> > > > > not, and that's where the epoch comes in. There's two reasons for an
> > > > > epoch:
> > > > > - We need it internally because I'm not goinig to wire a new return
> > > > > value through hundreds of connector probe functions. It's much easier
> > > > > to have an epoch counter which we set from e.g. drm_set_edid and
> > > > > similar functions that update probe state.
> > > > 
> > > > I don't think I'm following what issue this is trying to solve
> > > > internally.
> > > 
> > > So I'm assuming that if we handle a hotplug, we only want to generate
> > > one uevent for that, not one for every little thing that changed.
> > > There's two ways to implement this logic:
> > > - With some epoch counter and a helper function you can call everytime
> > > something changed (e.g. status, or edid, or anything else we care
> > > about e.g. from dp aux). This won't need much (if any) driver changes,
> > > because we can just put these into the relevant helper/core functions
> > > (like edid update, or dp aux reading or whatever).
> > > - Wiring a new return value through the entire stack (and _all_ the
> > > kms drivers) so that the probe helpers could aggregate this like they
> > > currently do.
> > > 
> > > One of these is a lot less typing.
> > > 
> > > > > - If userspace misses an event and there's no epoch, we're forcing
> > > > > userspace to reprobe everything. Use case would be if a compositor is
> > > > > switched away we probably don't want to piss of the current compositor
> > > > > by blocking it's own probe kernel calls by doing our own (probe is
> > > > > single-threaded in the kernel through the dev->mode_config.mutex). If
> > > > > it can read the epoch property (which it can do without forcing a
> > > > > reprobe) userspace would know which connectors it needs to check and
> > > > > reprobe.
> > > > > 
> > > > > Hence why epoch, it's a bit more robust userspace api. Ofc you could
> > > > > also require that userspace needs to keep parsing all uevents and make
> > > > > a list of all connectors it needs to reprobe when it's back to being
> > > > > the active compositor. But just comparing a current epoch with the one
> > > > > you cached from the last full probe is much easier.
> > > > 
> > > > Fair enough, I think it's a fine idea for robustness yes, but I think
> > > > we could also provide extra info in the uevent when relevant and not
> > > > rely on that entirely.
> > > 
> > > See above, with drmGetConnectorCurrent there's no need to provide more
> > > than what's needed in the uevent, since userspace can get everything
> > > else at the cost of one ioctl, without reprobing. With a bit of
> > > engineering work we could even avoid taking the expensive
> > > dev->mode_config.mutex lock for this fastpath.
> > > 
> > > > > Another thing: None of this we can for connectors with unreliable hdp.
> > > > > Or at least you'll piss of users if you cache always. The sad thing is
> > > > > that HDMI is unreliable, at least on some machines/screen combos (you
> > > > > never get a hpd irq if you plug in/unplug). So real compositors still
> > > > > need to reprobe when the user asks for it. igt can probably get away
> > > > > without reprobing.
> > > > 
> > > > I wonder how that is handled currently and how a user action can solve
> > > > the issue without any notification from the kernel. Maybe a need a
> > > > better understanding of that case to have a clearer idea.
> > > 
> > > User opens the screen configuration tool -> usually at that point the
> > > tool/compositor force a full reprobe, which then often triggers the
> > > automatic reconfiguring. E.g. on one laptop I have here when I plug in
> > > random shit projectors at conferences nothing happens, until I run
> > > xrandr, which triggers the full reprobe, which then makes the kernel
> > > realize something change, sending and uevent, which starts the
> > > automatic reconfigure machinery.
> > > 
> > > There's also the issue that there's machines with hpd storms (even on
> > > DP, where you really need hpd to work to be compliant), and we have to
> > > turn of the hpd irq to keep the machine useable.
> > 
> > Note that xrandr only works on X11. On Wayland, it won't.
> > 
> > Whether the user can actually do anything depends on the compositor. On
> > GNOME the D-Bus interface could probably force a re-probe when a
> > configuration tool is started or maybe with a "Rescan connectors"
> > button (not sure they'd like to have this in their UI). On KDE, Weston
> > and wlroots there is no way to do it.
> > 
> > As compositor writers, do we really need to provide a way for users to
> > force a reprobe? Can't the kernel do anything to handle these bad
> > screens?
> 
> Yeah, we defensively fall back to polling. Which isn't great from a power
> usage pov.
> 
> btw as long as compositors use drmGetConnector and not just
> drmGetConnectorCurrent you can trigger a full reprobe. If there's not way
> to trigger that they'll all have to add a "force probe" button sooner or
> later. But usually it's enough if you do a full reprobe when the user
> starts your config tool.

FWIW, some compositors (Weston, wlroots-based ones) don't have a
"graphical config tool", either because it's command-line (and event-
based, not poll-based) or because screen configuration is static (but
hotplug is supported). I guess we would need to expose some kind of
"rescan" command, which nobody will know about. Sigh.

> > > Cheers, Daniel
> > > 
> > > > Cheers,
> > > > 
> > > > Paul
> > > > 
> > > > > -Daniel
> > > > > 
> > > > > > Then we still have the legacy case:
> > > > > > HOTPLUG=1
> > > > > > 
> > > > > > where userspace is expected to reprobe all the connectors.
> > > > > > 
> > > > > > I think this would deserve to be a separate series on its own. So I am
> > > > > > proposing to take this one off your plate and come up with another
> > > > > > seres implementing this proposal. What do you think?
> > > > > > 
> > > > > > Cheers,
> > > > > > 
> > > > > > Paul
> > > > > > 
> > > > > > > v2:
> > > > > > >   Minor fixes at KDoc comments [Daniel]
> > > > > > > v3:
> > > > > > >   Check the property is really attached with connector [Daniel]
> > > > > > > 
> > > > > > > Signed-off-by: Ramalingam C <ramalingam.c at intel.com>
> > > > > > > Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> > > > > > > ---
> > > > > > >  drivers/gpu/drm/drm_sysfs.c | 35 +++++++++++++++++++++++++++++++++++
> > > > > > >  include/drm/drm_sysfs.h     |  5 ++++-
> > > > > > >  2 files changed, 39 insertions(+), 1 deletion(-)
> > > > > > > 
> > > > > > > diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> > > > > > > index 18b1ac442997..63fa951a20db 100644
> > > > > > > --- a/drivers/gpu/drm/drm_sysfs.c
> > > > > > > +++ b/drivers/gpu/drm/drm_sysfs.c
> > > > > > > @@ -21,6 +21,7 @@
> > > > > > >  #include <drm/drm_sysfs.h>
> > > > > > >  #include <drm/drmP.h>
> > > > > > >  #include "drm_internal.h"
> > > > > > > +#include "drm_crtc_internal.h"
> > > > > > > 
> > > > > > >  #define to_drm_minor(d) dev_get_drvdata(d)
> > > > > > >  #define to_drm_connector(d) dev_get_drvdata(d)
> > > > > > > @@ -320,6 +321,9 @@ void drm_sysfs_lease_event(struct drm_device *dev)
> > > > > > >   * Send a uevent for the DRM device specified by @dev.  Currently we only
> > > > > > >   * set HOTPLUG=1 in the uevent environment, but this could be expanded to
> > > > > > >   * deal with other types of events.
> > > > > > > + *
> > > > > > > + * Any new uapi should be using the drm_sysfs_connector_status_event()
> > > > > > > + * for uevents on connector status change.
> > > > > > >   */
> > > > > > >  void drm_sysfs_hotplug_event(struct drm_device *dev)
> > > > > > >  {
> > > > > > > @@ -332,6 +336,37 @@ void drm_sysfs_hotplug_event(struct drm_device *dev)
> > > > > > >  }
> > > > > > >  EXPORT_SYMBOL(drm_sysfs_hotplug_event);
> > > > > > > 
> > > > > > > +/**
> > > > > > > + * drm_sysfs_connector_status_event - generate a DRM uevent for connector
> > > > > > > + * property status change
> > > > > > > + * @connector: connector on which property status changed
> > > > > > > + * @property: connector property whoes status changed.
> > > > > > > + *
> > > > > > > + * Send a uevent for the DRM device specified by @dev.  Currently we
> > > > > > > + * set HOTPLUG=1 and connector id along with the attached property id
> > > > > > > + * related to the status change.
> > > > > > > + */
> > > > > > > +void drm_sysfs_connector_status_event(struct drm_connector *connector,
> > > > > > > +                                   struct drm_property *property)
> > > > > > > +{
> > > > > > > +     struct drm_device *dev = connector->dev;
> > > > > > > +     char hotplug_str[] = "HOTPLUG=1", conn_id[30], prop_id[30];
> > > > > > > +     char *envp[4] = { hotplug_str, conn_id, prop_id, NULL };
> > > > > > > +
> > > > > > > +     WARN_ON(!drm_mode_obj_find_prop_id(&connector->base,
> > > > > > > +                                        property->base.id));
> > > > > > > +
> > > > > > > +     snprintf(conn_id, ARRAY_SIZE(conn_id),
> > > > > > > +              "CONNECTOR=%u", connector->base.id);
> > > > > > > +     snprintf(prop_id, ARRAY_SIZE(prop_id),
> > > > > > > +              "PROPERTY=%u", property->base.id);
> > > > > > > +
> > > > > > > +     DRM_DEBUG("generating connector status event\n");
> > > > > > > +
> > > > > > > +     kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE, envp);
> > > > > > > +}
> > > > > > > +EXPORT_SYMBOL(drm_sysfs_connector_status_event);
> > > > > > > +
> > > > > > >  static void drm_sysfs_release(struct device *dev)
> > > > > > >  {
> > > > > > >       kfree(dev);
> > > > > > > diff --git a/include/drm/drm_sysfs.h b/include/drm/drm_sysfs.h
> > > > > > > index 4f311e836cdc..d454ef617b2c 100644
> > > > > > > --- a/include/drm/drm_sysfs.h
> > > > > > > +++ b/include/drm/drm_sysfs.h
> > > > > > > @@ -4,10 +4,13 @@
> > > > > > > 
> > > > > > >  struct drm_device;
> > > > > > >  struct device;
> > > > > > > +struct drm_connector;
> > > > > > > +struct drm_property;
> > > > > > > 
> > > > > > >  int drm_class_device_register(struct device *dev);
> > > > > > >  void drm_class_device_unregister(struct device *dev);
> > > > > > > 
> > > > > > >  void drm_sysfs_hotplug_event(struct drm_device *dev);
> > > > > > > -
> > > > > > > +void drm_sysfs_connector_status_event(struct drm_connector *connector,
> > > > > > > +                                   struct drm_property *property);
> > > > > > >  #endif
> > > > > > --
> > > > > > Paul Kocialkowski, Bootlin
> > > > > > Embedded Linux and kernel engineering
> > > > > > https://bootlin.com
> > > > > > 
> > > > --
> > > > Paul Kocialkowski, Bootlin
> > > > Embedded Linux and kernel engineering
> > > > https://bootlin.com
> > > >

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