drm/mediatek: fix kernel oops if no crtc is found

[ Upstream commit 4662817aed5a9d6c695658d0105d8ff4b84ac6cb ]

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@kernel.org>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Eugen Hristev <eugen.hristev@collabora.com>
Reviewed-by: Eugen Hristev <eugen.hristev@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230905084922.3908121-1-mwalle@kernel.org/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index 2d6a979afe8f95d00f85abda937ee54f2baa4fe2..cdd506c803733091173ca9df6baeffdaeffff18e 100644 (file)
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -421,6 +421,7 @@ 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())
@@ -495,7 +496,9 @@ 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");