On 2021-08-02 4:51 p.m., Alex Deucher wrote: > On Mon, Aug 2, 2021 at 4:31 AM Daniel Vetter <daniel@xxxxxxxx> wrote: >> >> On Mon, Aug 02, 2021 at 10:12:47AM +0200, Christian König wrote: >>> Am 02.08.21 um 09:43 schrieb Zhenneng Li: >>>> When primary bo is updated, crtc's pitch may >>>> have not been updated, this will lead to show >>>> disorder content when user changes display mode, >>>> we update crtc's pitch in page flip to avoid >>>> this bug. >>>> This refers to amdgpu's pageflip. >>> >>> Alex is the expert to ask about that code, but I'm not sure if that is >>> really correct for the old hardware. >>> >>> As far as I know the crtc's pitch should not change during a page flip, but >>> only during a full mode set. >>> >>> So could you elaborate a bit more how you trigger this? >> >> legacy page_flip ioctl only verifies that the fb->format stays the same. >> It doesn't check anything else (afair never has), this is all up to >> drivers to verify. >> >> Personally I'd say add a check to reject this, since testing this and >> making sure it really works everywhere is probably a bit much on this old >> hw. > > If just the pitch changed, that probably wouldn't be much of a > problem, but if the pitch is changing, that probably implies other > stuff has changed as well and we'll just be chasing changes. I agree > it would be best to just reject anything other than updating the > scanout address. FWIW, that means page flipping cannot be used in some cases which work fine by changing the pitch, which can result in tearing: https://gitlab.freedesktop.org/xorg/xserver/-/issues/839 (which says the i915 driver handles this as well). -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and X developer
