Re: [PATCH v10 2/9] drm/bridge: fsl-ldb: Get the next non-panel bridge

[Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>]

Hi Luca,

Thanks for looking over this patch.

On Fri, Oct 30, 2026 at 09:29:39AM +0100, Luca Ceresoli wrote:
> Hello Laurentiu,
> 
> > The next bridge in bridge chain could be a panel bridge or a non-panel
> > bridge.  Use devm_drm_of_get_bridge() to replace the combination
> > function calls of of_drm_find_panel() and devm_drm_panel_bridge_add()
> > to get either a panel bridge or a non-panel bridge, instead of getting
> > a panel bridge only.
> 
> Since commit b7797081ccfe ("drm/panel: embed a drm_bridge into every
> drm_panel") there is no such thing as a panel_bridge. Now every panel just
> embeds a bridge, and there is no reason to use the panel_bridge API. All
> bridges/encoders/whoever needing to interact with "the next component, be
> it a bridge or a panel" should just use the bridge API.
> 
> The old panel_bridge APIs are deprecated [0] and by now they are just
> complicated wrappers to the bridge API.
> 
> I'm addressing the conversion to bridge API and eventual removal of the
> deprecated panel_bridge API as time permits (but pathces would be
> welcome). This driver has already been converted by commit 802372cf316a
> ("drm/bridge: fsl-ldb: don't create a panel_bridge"), so this patch is
> basically not changing anything: it's still getting a pointer to the next
> bridge, but switches to a slightly more complicated implementation.
> 
> So I'd drop this patch.

Agreed

> 
> Still it's good to get rid of the obsolete "panel" wording because now we
> don't interact with a panel aymore, see below.

OK, I'll replace this patch with one addressing your comments below.

> 
> [0] https://gitlab.freedesktop.org/drm/misc/kernel/-/blob/drm-misc-next/Documentation/gpu/todo.rst#remove-panel_bridge-api-functions
> 
> >
> > Signed-off-by: Liu Ying <victor.liu@nxp.com>
> > Signed-off-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>
> >
> > diff --git a/drivers/gpu/drm/bridge/fsl-ldb.c b/drivers/gpu/drm/bridge/fsl-ldb.c
> > index 7ec84c81cd78..52ae7f5b63c7 100644
> > --- a/drivers/gpu/drm/bridge/fsl-ldb.c
> > +++ b/drivers/gpu/drm/bridge/fsl-ldb.c
> > @@ -294,8 +294,8 @@ static const struct drm_bridge_funcs funcs = {
> >  static int fsl_ldb_probe(struct platform_device *pdev)
> >  {
> >  	struct device *dev = &pdev->dev;
> > -	struct device_node *panel_node;
> 
> This could be renamed remote_bridge, or next_bridge_node, or the like.
> 
> >  	struct device_node *remote1, *remote2;
> > +	struct drm_bridge *next_bridge;
> >  	struct fsl_ldb *fsl_ldb;
> >  	int dual_link;
> >
> > @@ -318,19 +318,16 @@ static int fsl_ldb_probe(struct platform_device *pdev)
> >  	if (IS_ERR(fsl_ldb->regmap))
> >  		return PTR_ERR(fsl_ldb->regmap);
> >
> > -	/* Locate the remote ports and the panel node */
> > +	/* Locate the remote ports. */
> 
> This is OK.
> 
> >  	remote1 = of_graph_get_remote_node(dev->of_node, 1, 0);
> >  	remote2 = of_graph_get_remote_node(dev->of_node, 2, 0);
> >  	fsl_ldb->ch0_enabled = (remote1 != NULL);
> >  	fsl_ldb->ch1_enabled = (remote2 != NULL);
> > -	panel_node = of_node_get(remote1 ? remote1 : remote2);
> 
> I'd leave it as is, it's just less code (and more efficient FWIW)
> than... see below (*)
> 
> >  	of_node_put(remote1);
> >  	of_node_put(remote2);
> >
> > -	if (!fsl_ldb->ch0_enabled && !fsl_ldb->ch1_enabled) {
> > -		of_node_put(panel_node);
> > -		return dev_err_probe(dev, -ENXIO, "No panel node found");
> > -	}
> > +	if (!fsl_ldb->ch0_enabled && !fsl_ldb->ch1_enabled)
> > +		return dev_err_probe(dev, -ENXIO, "No next bridge node found");
> 
> This can be simplified by using a clenaup action on panel_node (or whatever
> the new name will be), so the of_node_put() would disappear. See for
> example commit 23bc92902edd ("drm/mxsfb/lcdif: simplify ep pointer
> management using __free").
> 
> 
> > @@ -339,10 +336,14 @@ static int fsl_ldb_probe(struct platform_device *pdev)
> >  	if (of_property_present(dev->of_node, "nxp,enable-termination-resistor"))
> >  		fsl_ldb->use_termination_resistor = true;
> >
> > -	fsl_ldb->bridge.next_bridge = of_drm_find_and_get_bridge(panel_node);
> > -	of_node_put(panel_node);
> > -	if (!fsl_ldb->bridge.next_bridge)
> > -		return -ENODEV;
> > +	next_bridge = of_drm_get_bridge_by_endpoint(dev->of_node,
> > +						    fsl_ldb->ch0_enabled ? 1 : 2,
> > +						    0);
> 
> (*) ...this code.
> 
> > +	if (IS_ERR(next_bridge))
> > +		return dev_err_probe(dev, PTR_ERR(next_bridge),
> > +				     "failed to get next bridge\n");
> > +
> > +	fsl_ldb->bridge.next_bridge = next_bridge;
> >
> >  	if (fsl_ldb_is_dual(fsl_ldb)) {
> >  		struct device_node *port1, *port2;
> 
> Luca
> 
> -- 
> Luca Ceresoli, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
> 

-- 
Thanks,
Laurentiu