Re: [PATCH v4 10/11] drm: zynqmp_dp: switch to of_drm_get_bridge_by_endpoint()

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Luca,

Thank you for the patch.

On Mon, May 04, 2026 at 12:45:13PM +0200, Luca Ceresoli wrote:
> This driver calls drm_of_find_panel_or_bridge() with a NULL pointer in the
> @panel parameter, thus using a reduced feature set of that function.
> Replace this call with the simpler of_drm_get_bridge_by_endpoint().
> 
> Since of_drm_get_bridge_by_endpoint() increases the refcount of the
> returned bridge, ensure it is put on removal. To achieve this, instead of
> adding an explicit drm_bridge_put(), migrate to the bridge::next_bridge
> pointer which is automatically put when the bridge is eventually freed.
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
> ---
> 
> Changes in v4:
> - fix missing assignment
> 
> Changes in v3:
> - fix ERR_PTR deref when -ENODEV is returned
> ---
>  drivers/gpu/drm/xlnx/zynqmp_dp.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> index 379180fb3004..fd30491a6697 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> @@ -353,7 +353,6 @@ struct zynqmp_dp_train_set_priv {
>   * @lock: Mutex protecting this struct and register access (but not AUX)
>   * @irq: irq
>   * @bridge: DRM bridge for the DP encoder
> - * @next_bridge: The downstream bridge
>   * @test: Configuration for test mode
>   * @config: IP core configuration from DTS
>   * @aux: aux channel
> @@ -385,7 +384,6 @@ struct zynqmp_dp {
>  	struct completion aux_done;
>  	struct mutex lock;
>  
> -	struct drm_bridge *next_bridge;
>  	struct device *dev;
>  	struct zynqmp_dpsub *dpsub;
>  	void __iomem *iomem;
> @@ -1494,8 +1492,8 @@ static int zynqmp_dp_bridge_attach(struct drm_bridge *bridge,
>  		return ret;
>  	}
>  
> -	if (dp->next_bridge) {
> -		ret = drm_bridge_attach(encoder, dp->next_bridge,
> +	if (dp->bridge.next_bridge) {
> +		ret = drm_bridge_attach(encoder, dp->bridge.next_bridge,
>  					bridge, flags);
>  		if (ret < 0)
>  			goto error;
> @@ -2461,10 +2459,15 @@ int zynqmp_dp_probe(struct zynqmp_dpsub *dpsub)
>  	 * Acquire the next bridge in the chain. Ignore errors caused by port@5
>  	 * not being connected for backward-compatibility with older DTs.
>  	 */
> -	ret = drm_of_find_panel_or_bridge(dp->dev->of_node, 5, 0, NULL,
> -					  &dp->next_bridge);
> -	if (ret < 0 && ret != -ENODEV)
> -		goto err_reset;
> +	dp->bridge.next_bridge = of_drm_get_bridge_by_endpoint(dp->dev->of_node, 5, 0);
> +	if (IS_ERR(dp->bridge.next_bridge)) {
> +		if (PTR_ERR(dp->bridge.next_bridge) == -ENODEV) {
> +			dp->bridge.next_bridge = NULL;
> +		} else {
> +			ret = PTR_ERR(dp->bridge.next_bridge);
> +			goto err_reset;
> +		}

I would find

		if (PTR_ERR(dp->bridge.next_bridge) != -ENODEV) {
			ret = PTR_ERR(dp->bridge.next_bridge);
			goto err_reset;
		}

		dp->bridge.next_bridge = NULL;

easier to read. Up to you.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> +	}
>  
>  	/* Initialize the hardware. */
>  	dp->config.misc0 &= ~ZYNQMP_DP_MAIN_STREAM_MISC0_SYNC_LOCK;

-- 
Regards,

Laurent Pinchart