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

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Message-ID: <20240718082410.204459-1-angelogioacchino.delregno@collabora.com>
Date: Thu, 18 Jul 2024 10:24:10 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: chunkuang.hu@...nel.org
Cc: p.zabel@...gutronix.de,
	airlied@...il.com,
	daniel@...ll.ch,
	matthias.bgg@...il.com,
	angelogioacchino.delregno@...labora.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: [PATCH] drm/mediatek: Set sensible cursor width/height values to fix crash

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;
 
 	/* Use OVL device for all DMA memory allocations */
 	crtc = drm_crtc_from_index(drm, 0);
-- 
2.45.2