linux-kernel - Re: [PATCH 11/11] drm/bridge: tc358768: Add DRM_BRIDGE_ATTACH_NO

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Date:   Mon, 14 Aug 2023 16:29:22 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Maxim Schwalm <maxim.schwalm@...il.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Péter Ujfalusi <peter.ujfalusi@...il.com>,
        Francesco Dolcini <francesco@...cini.it>,
        Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Aradhya Bhatia <a-bhatia1@...com>
Subject: Re: [PATCH 11/11] drm/bridge: tc358768: Add
 DRM_BRIDGE_ATTACH_NO_CONNECTOR support

Hi Sam,

On 14/08/2023 13:10, Sam Ravnborg wrote:
> Hi Tomi,
> 
>>  From c13c691bd8826b978325575be9a87f577b83b86b Mon Sep 17 00:00:00 2001
>> From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>> Date: Mon, 14 Aug 2023 13:02:23 +0300
>> Subject: [PATCH] drm/bridge: tc358768: fix 'Add DRM_BRIDGE_ATTACH_NO_CONNECTOR
>>   support'
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>> ---
>>   drivers/gpu/drm/bridge/tc358768.c | 56 +++++++++++++------------------
>>   1 file changed, 24 insertions(+), 32 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
>> index 82ea4d9a814a..9705ce1bd028 100644
>> --- a/drivers/gpu/drm/bridge/tc358768.c
>> +++ b/drivers/gpu/drm/bridge/tc358768.c
>> @@ -455,8 +455,6 @@ static int tc358768_dsi_host_detach(struct mipi_dsi_host *host,
>>   	struct tc358768_priv *priv = dsi_host_to_tc358768(host);
>>   
>>   	drm_bridge_remove(&priv->bridge);
>> -	if (priv->output.panel)
>> -		drm_panel_bridge_remove(priv->output.next_bridge);
>>   
>>   	return 0;
>>   }
>> @@ -531,49 +529,42 @@ static int tc358768_bridge_attach(struct drm_bridge *bridge,
>>   				  enum drm_bridge_attach_flags flags)
>>   {
>>   	struct tc358768_priv *priv = bridge_to_tc358768(bridge);
>> +	struct drm_bridge *next_bridge;
>> +	struct drm_panel *panel;
>> +	int ret;
>>   
>>   	if (!drm_core_check_feature(bridge->dev, DRIVER_ATOMIC)) {
>>   		dev_err(priv->dev, "needs atomic updates support\n");
>>   		return -ENOTSUPP;
>>   	}
>>   
>> -	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
>> -		struct device_node *node;
>> -
>> -		/* Get the next bridge, connected to port@1. */
>> -		node = of_graph_get_remote_node(priv->dev->of_node, 1, -1);
>> -		if (!node)
>> -			return -ENODEV;
>> -
>> -		priv->output.next_bridge = of_drm_find_bridge(node);
>> -		of_node_put(node);
>> -		if (!priv->output.next_bridge)
>> -			return -EPROBE_DEFER;
>> -	} else {
>> -		struct drm_bridge *bridge;
>> -		struct drm_panel *panel;
>> -		int ret;
>> -
>> -		ret = drm_of_find_panel_or_bridge(priv->dev->of_node, 1, 0,
>> -						  &panel, &bridge);
>> -		if (ret)
>> -			return ret;
>> -
>> -		if (panel) {
>> -			bridge = drm_panel_bridge_add_typed(panel,
>> -				DRM_MODE_CONNECTOR_DSI);
>> -			if (IS_ERR(bridge))
>> -				return PTR_ERR(bridge);
>> -		}
>> +	ret = drm_of_find_panel_or_bridge(priv->dev->of_node, 1, -1, &panel,
>> +					  &next_bridge);
> 
> I think the right way is to wrap the panel in a bridge,
> so something like:
> 
> 	next_bridge = devm_drm_of_get_bridge(dev, priv->dev->of_node, 1, -1)
> 
> 	if (IS_ERR(next_bridge))
> 		return ...
> 	priv->output.next_bridge = next_bridge;

I tried that, but I had trouble with the cleanup side.

In the fixup patch I attached in my reply to Maxim I used 
drm_of_find_panel_or_bridge() + drm_panel_bridge_add_typed(), and on 
bridge_detach callback I used drm_panel_bridge_remove() (if there is a 
panel). This worked for me, but it does feel like a bit too much work 
for a driver to do.

  Tomi