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

[Eugen Hristev]

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 at kernel.org>
> Reviewed-by: Nícolas F. R. A. Prado <nfraprado at collabora.com>
> Tested-by: Nícolas F. R. A. Prado <nfraprado at collabora.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>

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

Tested-by: Eugen Hristev <eugen.hristev at collabora.com>
Reviewed-by: Eugen Hristev <eugen.hristev at collabora.com>

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");