Re: [PATCH] drm/radeon: Update pitch for page flip

From: Alex Deucher <alexdeucher@gmail.com>
To: "Michel Dänzer" <michel@daenzer.net>
Cc: "Christian König" <christian.koenig@amd.com>,
	"Zhenneng Li" <lizhenneng@kylinos.cn>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Pan, Xinhui" <Xinhui.Pan@amd.com>,
	"David Airlie" <airlied@linux.ie>,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
	"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Daniel Vetter" <daniel@ffwll.ch>
Subject: Re: [PATCH] drm/radeon: Update pitch for page flip
Date: Tue, 3 Aug 2021 10:49:39 -0400	[thread overview]
Message-ID: <CADnq5_MJ=m2_VvzCQ7wJaFx2=OfFfLpoJtc_Ofb+a-v3eujtXg@mail.gmail.com> (raw)
In-Reply-To: <6a34fcc3-0aa3-85ff-21c4-86b9b5a48fd5@daenzer.net>

On Tue, Aug 3, 2021 at 4:34 AM Michel Dänzer <michel@daenzer.net> wrote:
>
> On 2021-08-02 4:51 p.m., Alex Deucher wrote:
> > On Mon, Aug 2, 2021 at 4:31 AM Daniel Vetter <daniel@ffwll.ch> 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).
>

Ok.  In that case, @Zhenneng can you update all of the pitch in all of
the page_flip functions in radeon rather than just the evergreen one?

Thanks,

Alex

>
> --
> Earthling Michel Dänzer               |               https://redhat.com
> Libre software enthusiast             |             Mesa and X developer