[PATCH v2 1/3] drm/mediatek: drm_ddp_comp: Fix and cleanup DDP component CRTC search

[AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>]

Finding a possible CRTC by DDP component is done by first checking
static routes in three paths (main, external, third/extra path) and
then, if not found, we check for dynamic connection on a per-route
basis because, for example, on some SoCs the main route may output
to either a DSI display or DisplayPort and this is finally done by
assigning a CRTC mask to `possible_crtcs`, found with function
mtk_drm_find_comp_in_ddp_conn_path(): being that a mask the possible
values are BIT(x) and, if no CRTC is possible, zero.

Problem is, both mtk_drm_find_possible_crtc_by_comp() and the
aforementioned function are trying to return a negative error value
(but it's unsigned int, so the value is never negative!) if no CRTC
was found, which is wrong for multiple obvious reasons.

Cleanup both functions, so that:
 - mtk_drm_find_comp_in_ddp_conn_path() returns a signed integer
   with a negative number for error, or a bit/bitmask of the found
   possible CRTC; and
 - mtk_drm_find_possible_crtc_by_comp() always returns either a
   bitmask of the possible CRTC, or zero if none available.

Fixes: 01389b324c97 ("drm/mediatek: Add connector dynamic selection capability")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c | 44 ++++++++++-----------
 1 file changed, 21 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
index a515e96cfefc..82d7a6887f44 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
@@ -514,29 +514,25 @@ static bool mtk_drm_find_comp_in_ddp(struct device *dev,
 	return false;
 }
 
-static unsigned int mtk_drm_find_comp_in_ddp_conn_path(struct device *dev,
-						       const struct mtk_drm_route *routes,
-						       unsigned int num_routes,
-						       struct mtk_ddp_comp *ddp_comp)
+static int mtk_drm_find_comp_in_ddp_conn_path(struct device *dev,
+					      const struct mtk_drm_route *routes,
+					      unsigned int num_routes,
+					      struct mtk_ddp_comp *ddp_comp)
 {
-	int ret;
-	unsigned int i;
+	int i;
 
-	if (!routes) {
-		ret = -EINVAL;
-		goto err;
+	if (!routes || !num_routes) {
+		DRM_ERROR("No connection routes specified!\n");
+		return -EINVAL;
 	}
 
 	for (i = 0; i < num_routes; i++)
 		if (dev == ddp_comp[routes[i].route_ddp].dev)
 			return BIT(routes[i].crtc_id);
 
-	ret = -ENODEV;
-err:
-
-	DRM_INFO("Failed to find comp in ddp table, ret = %d\n", ret);
+	DRM_ERROR("Failed to find component in ddp table\n");
 
-	return 0;
+	return -ENODEV;
 }
 
 int mtk_ddp_comp_get_id(struct device_node *node,
@@ -558,22 +554,24 @@ unsigned int mtk_drm_find_possible_crtc_by_comp(struct drm_device *drm,
 						struct device *dev)
 {
 	struct mtk_drm_private *private = drm->dev_private;
-	unsigned int ret = 0;
+	int ret;
 
 	if (mtk_drm_find_comp_in_ddp(dev, private->data->main_path, private->data->main_len,
 				     private->ddp_comp))
-		ret = BIT(0);
+		return BIT(0);
 	else if (mtk_drm_find_comp_in_ddp(dev, private->data->ext_path,
 					  private->data->ext_len, private->ddp_comp))
-		ret = BIT(1);
+		return BIT(1);
 	else if (mtk_drm_find_comp_in_ddp(dev, private->data->third_path,
 					  private->data->third_len, private->ddp_comp))
-		ret = BIT(2);
-	else
-		ret = mtk_drm_find_comp_in_ddp_conn_path(dev,
-							 private->data->conn_routes,
-							 private->data->num_conn_routes,
-							 private->ddp_comp);
+		return BIT(2);
+
+	ret = mtk_drm_find_comp_in_ddp_conn_path(dev, private->data->conn_routes,
+						 private->data->num_conn_routes,
+						 private->ddp_comp);
+	/* No CRTC is available: return a zero mask */
+	if (ret < 0)
+		return 0;
 
 	return ret;
 }
-- 
2.44.0