Re: [PATCH v4 1/2] drm/mediatek: fix kernel oops if no crtc is found

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On 9/5/23 11:49, Michael Walle wrote:
drm_crtc_from_index(0) might return NULL if there are no CRTCs
registered at all which will lead to a kernel oops in
mtk_drm_crtc_dma_dev_get(). Add the missing return value check.

Fixes: 0d9eee9118b7 ("drm/mediatek: Add drm ovl_adaptor sub driver for MT8195")
Signed-off-by: Michael Walle <mwalle@xxxxxxxxxx>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>
Tested-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>

I tried this patch as well, hit the crash during my tests. I also reviewed your changes

Tested-by: Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx>
Reviewed-by: Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx>

Eugen

---
v4:
  - collected tags
v3:
  - none
v2:
  - collected tags
  - fixed typos
---
  drivers/gpu/drm/mediatek/mtk_drm_drv.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index 93552d76b6e7..2c582498817e 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -420,6 +420,7 @@ static int mtk_drm_kms_init(struct drm_device *drm)
  	struct mtk_drm_private *private = drm->dev_private;
  	struct mtk_drm_private *priv_n;
  	struct device *dma_dev = NULL;
+	struct drm_crtc *crtc;
  	int ret, i, j;
if (drm_firmware_drivers_only())
@@ -494,7 +495,9 @@ static int mtk_drm_kms_init(struct drm_device *drm)
  	}
/* Use OVL device for all DMA memory allocations */
-	dma_dev = mtk_drm_crtc_dma_dev_get(drm_crtc_from_index(drm, 0));
+	crtc = drm_crtc_from_index(drm, 0);
+	if (crtc)
+		dma_dev = mtk_drm_crtc_dma_dev_get(crtc);
  	if (!dma_dev) {
  		ret = -ENODEV;
  		dev_err(drm->dev, "Need at least one OVL device\n");




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