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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Tue, 3 Aug 2021 10:49:39 -0400
Message-ID: <CADnq5_MJ=m2_VvzCQ7wJaFx2=OfFfLpoJtc_Ofb+a-v3eujtXg@mail.gmail.com>
Subject: Re: [PATCH] drm/radeon: Update pitch for page flip
To:     =?UTF-8?Q?Michel_D=C3=A4nzer?= <michel@daenzer.net>
Cc:     =?UTF-8?Q?Christian_K=C3=B6nig?= <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>
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On Tue, Aug 3, 2021 at 4:34 AM Michel D=C3=A4nzer <michel@daenzer.net> wrot=
e:
>
> 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 K=C3=B6nig 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 i=
s
> >>> really correct for the old hardware.
> >>>
> >>> As far as I know the crtc's pitch should not change during a page fli=
p, 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 sam=
e.
> >> 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 fi=
ne by changing the pitch, which can result in tearing: https://gitlab.freed=
esktop.org/xorg/xserver/-/issues/839 (which says the i915 driver handles th=
is 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 D=C3=A4nzer               |               https://redhat=
.com
> Libre software enthusiast             |             Mesa and X developer