linux-kernel - Re: [PATCH v7 2/6] drm/of: Make drm_of_find_panel_or

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Message-ID: <20200616012652.GG1629@pendragon.ideasonboard.com>
Date:   Tue, 16 Jun 2020 04:26:52 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/6] drm/of: Make drm_of_find_panel_or_bridge() to
 check graph's presence

Hi Dmitry,

Thank you for the patch.

On Sun, Jun 14, 2020 at 08:22:30PM +0300, Dmitry Osipenko wrote:
> When graph isn't defined in a device-tree, the of_graph_get_remote_node()
> prints a noisy error message, telling that port node is not found. This is
> undesirable behaviour in our case because absence of a panel/bridge graph
> is a valid case. Let's check presence of the local port in a device-tree
> before proceeding with parsing the graph.
> 
> Reviewed-by: Sam Ravnborg <sam@...nborg.org>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/gpu/drm/drm_of.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> index b50b44e76279..e0652c38f357 100644
> --- a/drivers/gpu/drm/drm_of.c
> +++ b/drivers/gpu/drm/drm_of.c
> @@ -239,13 +239,24 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
>  				struct drm_bridge **bridge)
>  {
>  	int ret = -EPROBE_DEFER;
> -	struct device_node *remote;
> +	struct device_node *local, *remote;
>  
>  	if (!panel && !bridge)
>  		return -EINVAL;
>  	if (panel)
>  		*panel = NULL;
>  
> +	/*
> +	 * of_graph_get_remote_node() produces a noisy error message if port
> +	 * node isn't found and the absence of the port is a legit case here,
> +	 * so at first we silently check presence of the local port.
> +	 */
> +	local = of_graph_get_local_port(np);
> +	if (!local)
> +		return -ENODEV;
> +
> +	of_node_put(local);
> +

The code looks fine, but you may want to take into account my proposal
in 1/7 to instead create a of_graph_has_port() function. The could would
be simpler here.

>  	remote = of_graph_get_remote_node(np, port, endpoint);
>  	if (!remote)
>  		return -ENODEV;

-- 
Regards,

Laurent Pinchart