drm/mediatek: dpi/dsi: Fix possible_crtcs calculation

mtk_find_possible_crtcs() assumes that the main path will always have
the CRTC with id 0, the ext id 1 and the third id 2. This is only true
if the paths are all available. But paths are optional (see also
comment in mtk_drm_kms_init()), e.g. the main path might not be enabled
or available at all. Then the CRTC IDs will shift one up, e.g. ext will
be 0 and the third path will be 1.

To fix that, dynamically calculate the IDs by the presence of the paths.

While at it, make the return code a signed one and return -ENODEV if no
path is found and handle the error in the callers.

Fixes: 5aa8e7647676 ("drm/mediatek: dpi/dsi: Change the getting possible_crtc way")
Suggested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Michael Walle <mwalle@kernel.org>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240606092122.2026313-1-mwalle@kernel.org/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
index c255559cc56e..b6e3c011a12d 100644
--- a/drivers/gpu/drm/mediatek/mtk_dsi.c
+++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
@@ -837,7 +837,10 @@ static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *dsi)
 		return ret;
 	}
 
-	dsi->encoder.possible_crtcs = mtk_find_possible_crtcs(drm, dsi->host.dev);
+	ret = mtk_find_possible_crtcs(drm, dsi->host.dev);
+	if (ret < 0)
+		goto err_cleanup_encoder;
+	dsi->encoder.possible_crtcs = ret;
 
 	ret = drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL,
 				DRM_BRIDGE_ATTACH_NO_CONNECTOR);