linux-kernel - Re: [PATCH 3/5] drm/bridge: simple-bridge: Allow acquiring the next bridge with fwnode API

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Message-ID: <20240123151835.GO10679@pendragon.ideasonboard.com>
Date: Tue, 23 Jan 2024 17:18:35 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc: David Airlie <airlied@...il.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Daniel Vetter <daniel@...ll.ch>, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] drm/bridge: simple-bridge: Allow acquiring the next
 bridge with fwnode API

Hello Sui,

On Tue, Jan 23, 2024 at 08:18:22PM +0800, Sui Jingfeng wrote:
> On 2024/1/23 09:18, Laurent Pinchart wrote:
> > On Tue, Jan 23, 2024 at 12:32:18AM +0800, Sui Jingfeng wrote:
> >> Which make it possible to use this driver on non-DT based systems,
> >> meanwhile, made no functional changes for DT based systems.
> >>
> >> Signed-off-by: Sui Jingfeng <sui.jingfeng@...ux.dev>
> >> ---
> >>   drivers/gpu/drm/bridge/simple-bridge.c | 51 ++++++++++++++++++++++----
> >>   1 file changed, 44 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/bridge/simple-bridge.c b/drivers/gpu/drm/bridge/simple-bridge.c
> >> index 595f672745b9..cfea5a67cc5b 100644
> >> --- a/drivers/gpu/drm/bridge/simple-bridge.c
> >> +++ b/drivers/gpu/drm/bridge/simple-bridge.c
> >> @@ -184,6 +184,39 @@ static const void *simple_bridge_get_match_data(const struct device *dev)
> >>   	return NULL;
> >>   }
> >>   
> >> +static int simple_bridge_get_next_bridge_by_fwnode(struct device *dev,
> >> +						   struct drm_bridge **next_bridge)
> >> +{
> >> +	struct drm_bridge *bridge;
> >> +	struct fwnode_handle *ep;
> >> +	struct fwnode_handle *remote;
> >> +
> >> +	ep = fwnode_graph_get_endpoint_by_id(dev->fwnode, 1, 0, 0);
> >> +	if (!ep) {
> >> +		dev_err(dev, "The endpoint is unconnected\n");
> >> +		return -EINVAL;
> >> +	}
> >> +
> >> +	remote = fwnode_graph_get_remote_port_parent(ep);
> >> +	fwnode_handle_put(ep);
> >> +	if (!remote) {
> >> +		dev_err(dev, "No valid remote node\n");
> >> +		return -ENODEV;
> >> +	}
> >> +
> >> +	bridge = drm_bridge_find_by_fwnode(remote);
> >> +	fwnode_handle_put(remote);
> >> +
> >> +	if (!bridge) {
> >> +		dev_warn(dev, "Next bridge not found, deferring probe\n");
> >> +		return -EPROBE_DEFER;
> >> +	}
> >> +
> >> +	*next_bridge = bridge;
> >> +
> >> +	return 0;
> >> +}
> >> +
> >
> > Hmmmm yes, this convinces me further that we should switch to fwnode,
> > not implement fwnode and OF side-by-side.
> 
> OK, I'm agree with you.
> 
> But this means that I have to make the drm_bridge_find_by_fwnode() function works
> on both DT systems and non-DT systems. This is also means that we will no longer
> need to call of_drm_find_bridge() function anymore. This will eventually lead to
> completely remove of_drm_find_bridge()?

It would be replaced by fwnode_drm_find_bridge(). Although, if we need
to rename the function, I think it would be best to make have a drm_
prefix, maybe drm_bridge_find-by_fwnode() or something similar.

> As far as I can see, if I follow you suggestion, drm/bridge subsystem will
> encountering a *big* refactor. My 'side-by-side' approach allows co-exist.
> It is not really meant to purge OF. I feel it is a little bit of aggressive.
> 
> hello Maxime, are you watching this? what do you think?
> 
> >>   static int simple_bridge_probe(struct platform_device *pdev)
> >>   {
> >>   	struct simple_bridge *sbridge;
> >> @@ -199,14 +232,17 @@ static int simple_bridge_probe(struct platform_device *pdev)
> >>   	else
> >>   		sbridge->info = simple_bridge_get_match_data(&pdev->dev);
> >>   
> >> -	/* Get the next bridge in the pipeline. */
> >> -	remote = of_graph_get_remote_node(pdev->dev.of_node, 1, -1);
> >> -	if (!remote)
> >> -		return -EINVAL;
> >> -
> >> -	sbridge->next_bridge = of_drm_find_bridge(remote);
> >> -	of_node_put(remote);
> >> +	if (pdev->dev.of_node) {
> >> +		/* Get the next bridge in the pipeline. */
> >> +		remote = of_graph_get_remote_node(pdev->dev.of_node, 1, -1);
> >> +		if (!remote)
> >> +			return -EINVAL;
> >>   
> >> +		sbridge->next_bridge = of_drm_find_bridge(remote);
> >> +		of_node_put(remote);
> >> +	} else {
> >> +		simple_bridge_get_next_bridge_by_fwnode(&pdev->dev, &sbridge->next_bridge);
> >> +	}
> >>   	if (!sbridge->next_bridge) {
> >>   		dev_dbg(&pdev->dev, "Next bridge not found, deferring probe\n");
> >>   		return -EPROBE_DEFER;
> >> @@ -231,6 +267,7 @@ static int simple_bridge_probe(struct platform_device *pdev)
> >>   	/* Register the bridge. */
> >>   	sbridge->bridge.funcs = &simple_bridge_bridge_funcs;
> >>   	sbridge->bridge.of_node = pdev->dev.of_node;
> >> +	sbridge->bridge.fwnode = pdev->dev.fwnode;
> >>   	sbridge->bridge.timings = sbridge->info->timings;
> >>   
> >>   	drm_bridge_add(&sbridge->bridge);

-- 
Regards,

Laurent Pinchart