linux-kernel - Re: [PATCH] drm: bridge: thc63lvd1024: Switch to use of_graph_get_remote

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Message-ID: <20240318153326.GD13682@pendragon.ideasonboard.com>
Date: Mon, 18 Mar 2024 17:33:26 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Robert Foss <rfoss@...nel.org>, Jonas Karlman <jonas@...boo.se>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: bridge: thc63lvd1024: Switch to use
 of_graph_get_remote_node()

Hi Sui,

Thank you for the patch.

On Sun, Mar 17, 2024 at 01:28:00AM +0800, Sui Jingfeng wrote:
> To reduce boilerplate, use of_graph_get_remote_node() helper instead of
> the hand-rolling code.
> 
> Signed-off-by: Sui Jingfeng <sui.jingfeng@...ux.dev>
> ---
>  drivers/gpu/drm/bridge/thc63lvd1024.c | 24 +++---------------------
>  1 file changed, 3 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/thc63lvd1024.c b/drivers/gpu/drm/bridge/thc63lvd1024.c
> index d4c1a601bbb5..5f99f9724081 100644
> --- a/drivers/gpu/drm/bridge/thc63lvd1024.c
> +++ b/drivers/gpu/drm/bridge/thc63lvd1024.c
> @@ -123,28 +123,10 @@ static int thc63_parse_dt(struct thc63_dev *thc63)
>  	struct device_node *endpoint;
>  	struct device_node *remote;
>  
> -	endpoint = of_graph_get_endpoint_by_regs(thc63->dev->of_node,
> -						 THC63_RGB_OUT0, -1);
> -	if (!endpoint) {
> -		dev_err(thc63->dev, "Missing endpoint in port@%u\n",
> -			THC63_RGB_OUT0);
> -		return -ENODEV;
> -	}
> -
> -	remote = of_graph_get_remote_port_parent(endpoint);
> -	of_node_put(endpoint);
> -	if (!remote) {
> -		dev_err(thc63->dev, "Endpoint in port@%u unconnected\n",
> -			THC63_RGB_OUT0);
> +	remote = of_graph_get_remote_node(thc63->dev->of_node,
> +					  THC63_RGB_OUT0, -1);
> +	if (!remote)

The old logic is equivalent to of_graph_get_remote_node(), but now the
driver will fail probing without an error message. That's not very nice
as it leads to difficult to debug problems. I would keep one dev_err()
here:

		dev_err(thc63->dev, "No remote endpoint for port@%u\n",
			THC63_RGB_OUT0);

As your patch has been merged already, would you like to post a
follow-up patch to fix this ?

>  		return -ENODEV;
> -	}
> -
> -	if (!of_device_is_available(remote)) {
> -		dev_err(thc63->dev, "port@%u remote endpoint is disabled\n",
> -			THC63_RGB_OUT0);
> -		of_node_put(remote);
> -		return -ENODEV;
> -	}
>  
>  	thc63->next = of_drm_find_bridge(remote);
>  	of_node_put(remote);

-- 
Regards,

Laurent Pinchart