On Tue, 15 Feb 2022 at 16:37, Simon Ser <contact@xxxxxxxxxxx> wrote: > > On Tuesday, February 15th, 2022 at 15:38, Emil Velikov <emil.l.velikov@xxxxxxxxx> wrote: > > > On Tue, 15 Feb 2022 at 13:55, Simon Ser <contact@xxxxxxxxxxx> wrote: > > > > > > On Tuesday, February 15th, 2022 at 13:04, Emil Velikov <emil.l.velikov@xxxxxxxxx> wrote: > > > > > > > Greetings everyone, > > > > > > > > Padron for joining in so late o/ > > > > > > > > On Tue, 8 Feb 2022 at 08:42, Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx> wrote: > > > > > > > > > > drm_dev_register() sets connector->registration_state to > > > > > DRM_CONNECTOR_REGISTERED and dev->registered to true. If > > > > > drm_connector_set_panel_orientation() is first called after > > > > > drm_dev_register(), it will fail several checks and results in following > > > > > warning. > > > > > > > > > > Add a function to create panel orientation property and set default value > > > > > to UNKNOWN, so drivers can call this function to init the property earlier > > > > > , and let the panel set the real value later. > > > > > > > > > > > > > The warning illustrates a genuine race condition, where userspace will > > > > read the old/invalid property value/state. So this patch masks away > > > > the WARNING without addressing the actual issue. > > > > Instead can we fix the respective drivers, so that no properties are > > > > created after drm_dev_register()? > > > > > > > > Longer version: > > > > As we look into drm_dev_register() it's in charge of creating the > > > > dev/sysfs nodes (et al). Note that connectors cannot disappear at > > > > runtime. > > > > For panel orientation, we are creating an immutable connector > > > > properly, meaning that as soon as drm_dev_register() is called we must > > > > ensure that the property is available (if applicable) and set to the > > > > correct value. > > > > > > Unfortunately we can't quite do this. To apply the panel orientation quirks we > > > need to grab the EDID of the eDP connector, and this happened too late in my > > > testing. > > > > > > What we can do is create the prop early during module load, and update it when > > > we read the EDID (at the place where we create it right now). User-space will > > > receive a hotplug event after the EDID is read, so will be able to pick up the > > > new value if any. > > > > Didn't quite get that, are you saying that a GETPROPERTY for the EDID, > > the ioctl blocks or that we get an empty EDID? > > I'm not referring to GETPROPERTY, I'm referring to the driver getting the EDID > from the sink (here, the eDP panel). In my experimentations with amdgpu I > noticed that the driver module load finished before the EDID was available to > the driver. Maybe other drivers behave differently and probe connectors when > loaded, not sure. > I see thanks. > > The EDID hotplug even thing is neat - sounds like it also signals on > > panel orientation, correct? > > On such an event, which properties userspace should be re-fetching - > > everything or guess randomly? > > > > Looking through the documentation, I cannot see a clear answer :-\ > > User-space should re-fetch *all* properties. In practice some user-space may > only be fetching some properties, but that should get fixed in user-space. > > Also the kernel can indicate that only a single connector changed via the > "CONNECTOR" uevent prop, or even a single connector property via "PROPERTY". > See [1] for a user-space implementation. But all of this is purely an optional > optimization. Re-fetching all properties is a bit slower (especially if some > drmModeGetConnector calls force-probe connectors) but works perfectly fine. > Looking at KDE/kwin (the one I'm running) - doesn't seem like it handles any of the three "HOTPLUG", "PROPERTY" or "CONNECTOR" uevents :-\ Skimming through GNOME/mutter - it handles "HOTPLUG", but not the optional ones. Guess we're in the clear wrt potential races, even though the documentation on the topic is lacklustre. > It would be nice to document, if you have the time feel free to send a patch > and CC danvet, pq and me. > Doubt I will have the time in the upcoming weeks, but I'll add it to my ever-growing TODO list :-P Thanks Emil
