Re: [PATCH v8 2/9] drm/bridge: fsl-ldb: Get the next non-panel bridge

Liu Ying
2026-03-06T07:35:43Z

On Wed, Mar 04, 2026 at 11:34:11AM +0000, Laurentiu Palcu wrote:
> From: Liu Ying <victor.liu@nxp.com>
>
> 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.
>
> Signed-off-by: Liu Ying <victor.liu@nxp.com>
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> Reviewed-by: Frank Li <Frank.Li@nxp.com>
> Reviewed-by: Francesco Valla <francesco@valla.it>
> Signed-off-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>
> ---
> drivers/gpu/drm/bridge/fsl-ldb.c | 31 +++++++++++--------------------
> 1 file changed, 11 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/fsl-ldb.c b/drivers/gpu/drm/bridge/fsl-ldb.c
> index 7b71cde173e0c..d59f26016de26 100644
> --- a/drivers/gpu/drm/bridge/fsl-ldb.c
> +++ b/drivers/gpu/drm/bridge/fsl-ldb.c
> @@ -15,7 +15,6 @@
> #include <drm/drm_atomic_helper.h>
> #include <drm/drm_bridge.h>
> #include <drm/drm_of.h>
> -#include <drm/drm_panel.h>
>
> #define LDB_CTRL_CH0_ENABLE BIT(0)
> #define LDB_CTRL_CH0_DI_SELECT BIT(1)
> @@ -86,7 +85,7 @@ static const struct fsl_ldb_devdata fsl_ldb_devdata[] = {
> struct fsl_ldb {
> struct device *dev;
> struct drm_bridge bridge;
> - struct drm_bridge *panel_bridge;
> + struct drm_bridge *next_bridge;
> struct clk *clk;
> struct regmap *regmap;
> const struct fsl_ldb_devdata *devdata;
> @@ -119,7 +118,7 @@ static int fsl_ldb_attach(struct drm_bridge *bridge,
> {
> struct fsl_ldb *fsl_ldb = to_fsl_ldb(bridge);
>
> - return drm_bridge_attach(encoder, fsl_ldb->panel_bridge,
> + return drm_bridge_attach(encoder, fsl_ldb->next_bridge,
> bridge, flags);
> }
>
> @@ -296,9 +295,7 @@ 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;
> struct device_node *remote1, *remote2;
> - struct drm_panel *panel;
> struct fsl_ldb *fsl_ldb;
> int dual_link;
>
> @@ -321,36 +318,30 @@ 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. */
> 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);
> 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");
>
> dev_dbg(dev, "Using %s\n",
> fsl_ldb_is_dual(fsl_ldb) ? "dual-link mode" :
> fsl_ldb->ch0_enabled ? "channel 0" : "channel 1");
>
> - panel = of_drm_find_panel(panel_node);
> - of_node_put(panel_node);
> - if (IS_ERR(panel))
> - return PTR_ERR(panel);
> -
> if (of_property_present(dev->of_node, "nxp,enable-termination-resistor"))
> fsl_ldb->use_termination_resistor = true;
>
> - fsl_ldb->panel_bridge = devm_drm_panel_bridge_add(dev, panel);
> - if (IS_ERR(fsl_ldb->panel_bridge))
> - return PTR_ERR(fsl_ldb->panel_bridge);
> -
> + fsl_ldb->next_bridge = devm_drm_of_get_bridge(dev, dev->of_node,
> + fsl_ldb->ch0_enabled ? 1 : 2,
> + 0);

Cc'ing Luca.

Since commit[1] added next_bridge pointer to struct drm_bridge, can you
use that pointer instead of fsl_ldb->next_bridge?
This would be similar to how the in-flight imx93-pdfc.c driver[2] does.

However, after looking at commit[1] closely, I wonder if we need to call
drm_bridge_get() for the next_bridge returned from devm_drm_of_get_bridge()
because drm_bridge_put() would be called for the next_bridge when this
bridge(the next_bridge's previous bridge) is freed in __drm_bridge_free().
@Luca, can you please comment here? I see your R-b tag on [2] where
drm_bridge_get() is not called, does it mean that we don't need to call
drm_bridge_get()?

[1] 3fdeae134ba9 drm/bridge: add next_bridge pointer to struct drm_bridge
[2] https://lore.kernel.org/all/20260303-v6-18-topic-imx93-parallel-display-v11-2-1b03733c8461@pengutronix.de/

> + if (IS_ERR(fsl_ldb->next_bridge))
> + return dev_err_probe(dev, PTR_ERR(fsl_ldb->next_bridge),
> + "failed to get next bridge\n");
>
> if (fsl_ldb_is_dual(fsl_ldb)) {
> struct device_node *port1, *port2;
>

--
Regards,
Liu Ying