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!) 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@collabora.com>
---
 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 a9b5a21cde2d..c13359eeb3cd 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
@@ -513,29 +513,25 @@ 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,
@@ -557,22 +553,24 @@ 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;
 }
-- 
2.43.0

Hi, Angelo:

On Thu, 2024-02-01 at 13:53 +0100, AngeloGioacchino Del Regno wrote:
> 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!) if no CRTC was found, which is wrong for
> multiple obvious reasons.

I does not find anywhere to return negative value. So this patch just
like a refine patch not bug fix.

Regards,
CK

> 
> 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@collabora.com>
> ---
>  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 a9b5a21cde2d..c13359eeb3cd 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> @@ -513,29 +513,25 @@ 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,
> @@ -557,22 +553,24 @@ 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;
>  }