On Tue, Jun 18, 2024 at 5:40 PM Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > > Hi, > > > On Mon, Jun 17, 2024 at 8:01 AM Alex Deucher <alexdeucher@xxxxxxxxx> wrote: > > > > On Wed, Jun 12, 2024 at 6:37 PM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > > > > > > Based on grepping through the source code this driver appears to be > > > missing a call to drm_atomic_helper_shutdown() at system shutdown > > > time. Among other things, this means that if a panel is in use that it > > > won't be cleanly powered off at system shutdown time. > > > > > > The fact that we should call drm_atomic_helper_shutdown() in the case > > > of OS shutdown/restart comes straight out of the kernel doc "driver > > > instance overview" in drm_drv.c. > > > > > > Suggested-by: Maxime Ripard <mripard@xxxxxxxxxx> > > > Cc: Alex Deucher <alexander.deucher@xxxxxxx> > > > Cc: Christian König <christian.koenig@xxxxxxx> > > > Cc: Xinhui Pan <Xinhui.Pan@xxxxxxx> > > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > > > --- > > > This commit is only compile-time tested. > > > > > > ...and further, I'd say that this patch is more of a plea for help > > > than a patch I think is actually right. I'm _fairly_ certain that > > > drm/amdgpu needs this call at shutdown time but the logic is a bit > > > hard for me to follow. I'd appreciate if anyone who actually knows > > > what this should look like could illuminate me, or perhaps even just > > > post a patch themselves! > > > > I'm not sure this patch makes sense or not. The driver doesn't really > > do a formal tear down in its shutdown routine, it just quiesces the > > hardware. What are the actual requirements of the shutdown function? > > In the past when we did a full driver tear down in shutdown, it > > delayed the shutdown sequence and users complained. > > The "inspiration" for this patch is to handle panels properly. > Specifically, panels often have several power/enable signals going to > them and often have requirements that these signals are powered off in > the proper order with the proper delays between them. While we can't > always do so when the system crashes / reboots in an uncontrolled way, > panel manufacturers / HW Engineers get upset if we don't power things > off properly during an orderly shutdown/reboot. When panels are > powered off badly it can cause garbage on the screen and, so I've been > told, can even cause long term damage to the panels over time. > > In Linux, some panel drivers have tried to ensure a proper poweroff of > the panel by handling the shutdown() call themselves. However, this is > ugly and panel maintainers want panel drivers to stop doing it. We > have removed the code doing this from most panels now [1]. Instead the > assumption is that the DRM modeset drivers should be calling > drm_atomic_helper_shutdown() which will make sure panels get an > orderly shutdown. > > For a lot more details, see the cover letter [2] which then contains > links to even more discussions about the topic. > > [1] https://lore.kernel.org/r/20240605002401.2848541-1-dianders@xxxxxxxxxxxx > [2] https://lore.kernel.org/r/20240612222435.3188234-1-dianders@xxxxxxxxxxxx I don't think it's an issue. We quiesce the hardware as if we were about to suspend the system (e.g., S3). For the display hardware we call drm_atomic_helper_suspend() as part of that sequence. Alex
