linux-kernel - Re: [PATCH] drm/mediatek: Set sensible cursor width/height values to fix crash

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Message-ID: <CAC=S1nigoJWAECBrm-Q=Co1-qd_yUhx3R4D9=dYeUV=gr5UYfQ@mail.gmail.com>
Date: Thu, 18 Jul 2024 17:27:33 +0800
From: Fei Shao <fshao@...omium.org>
To: Chen-Yu Tsai <wenst@...omium.org>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, chunkuang.hu@...nel.org, 
	p.zabel@...gutronix.de, airlied@...il.com, daniel@...ll.ch, 
	matthias.bgg@...il.com, shawn.sung@...iatek.com, ck.hu@...iatek.com, 
	dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kernel@...labora.com
Subject: Re: [PATCH] drm/mediatek: Set sensible cursor width/height values to
 fix crash

On Thu, Jul 18, 2024 at 4:49 PM Chen-Yu Tsai <wenst@...omium.org> wrote:
>
> (CC-ed Fei Shao)
>
> On Thu, Jul 18, 2024 at 4:24 PM AngeloGioacchino Del Regno
> <angelogioacchino.delregno@...labora.com> wrote:
> >
> > Hardware-speaking, there is no feature-reduced cursor specific
> > plane, so this driver reserves the last all Overlay plane as a
> > Cursor plane, but sets the maximum cursor width/height to the
> > maximum value that the full overlay plane can use.
> >
> > While this could be ok, it raises issues with common userspace
> > using libdrm (especially Mutter, but other compositors too) which
> > will crash upon performing allocations and/or using said cursor
> > plane.
> >
> > Reduce the maximum width/height for the cursor to 512x512 pixels,
> > value taken from IGT's maximum cursor size test, which succeeds.
> >
> > Fixes: a4c9410b31ca ("drm/mediatek: Set DRM mode configs accordingly")
> > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> > ---
> >  drivers/gpu/drm/mediatek/mtk_drm_drv.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > index 6f0b415a978d..b96763664c4f 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > @@ -540,8 +540,8 @@ static int mtk_drm_kms_init(struct drm_device *drm)
> >         }
> >
> >         /* IGT will check if the cursor size is configured */
> > -       drm->mode_config.cursor_width = drm->mode_config.max_width;
> > -       drm->mode_config.cursor_height = drm->mode_config.max_height;
> > +       drm->mode_config.cursor_width = 512;
> > +       drm->mode_config.cursor_height = 512;
>
> Fei already did the same (?) workaround downstream just recently.

Well, so another userspace gets confused...
I actually sent a separate userspace (i.e. Chrome) fix where I
encountered the issue, so I didn't proceed with upstreaming it in the
end.

This matches my preference in [1], so of course I'd like to see it
merged... if maintainers are okay with it.
Given I've tested the exact same change before:
Reviewed-by: Fei Shao <fshao@...omium.org>
Tested-by: Fei Shao <fshao@...omium.org>

[1]: https://lore.kernel.org/all/CAC=S1nhKPo5BUYJ_cHGz3OoPrWNh5eO8rhdyikLimsqSOrZ5Xg@mail.gmail.com/

Regards,
Fei
>
> OOTH, Intel recently added a feature for enumerating "suggested"
> cursor sizes. See https://patchwork.freedesktop.org/patch/583299/
>
> Not sure if other compositors will end up using it or not.
>
> ChenYu
>
> >         /* Use OVL device for all DMA memory allocations */
> >         crtc = drm_crtc_from_index(drm, 0);
> > --
> > 2.45.2
> >