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

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Message-ID: <CAGXv+5GBg73kWuiDt=9s7M4oJeHhWOF3bPY7Ju+qn1kJgNNaGw@mail.gmail.com>
Date: Thu, 18 Jul 2024 16:49:27 +0800
From: Chen-Yu Tsai <wenst@...omium.org>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: 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, 
	Fei Shao <fshao@...omium.org>
Subject: Re: [PATCH] drm/mediatek: Set sensible cursor width/height values to
 fix crash

(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.

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
>