linux-kernel - Re: [PATCH 1/3] drm/mediatek: drm_ddp_comp: Fix and cleanup DDP component CRTC search

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Message-ID: <72a1d501d001899eeac9b4c308a291f0fa86e935.camel@mediatek.com>
Date: Fri, 22 Mar 2024 07:30:30 +0000
From: CK Hu (胡俊光) <ck.hu@...iatek.com>
To: "angelogioacchino.delregno@...labora.com"
	<angelogioacchino.delregno@...labora.com>, "chunkuang.hu@...nel.org"
	<chunkuang.hu@...nel.org>
CC: "linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"wenst@...omium.org" <wenst@...omium.org>, "kernel@...labora.com"
	<kernel@...labora.com>, Nancy Lin (林欣螢)
	<Nancy.Lin@...iatek.com>, "daniel@...ll.ch" <daniel@...ll.ch>,
	"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Nathan Lu (呂東霖) <Nathan.Lu@...iatek.com>,
	"airlied@...il.com" <airlied@...il.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "matthias.bgg@...il.com"
	<matthias.bgg@...il.com>
Subject: Re: [PATCH 1/3] drm/mediatek: drm_ddp_comp: Fix and cleanup DDP
 component CRTC search

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@...labora.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;
>  }