linux-kernel - Re: [PATCH] drm/bridge: ldb: add support for an external bridge

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Message-ID: <1944228.tdWV9SEqCh@steina-w>
Date: Tue, 28 Oct 2025 13:27:37 +0100
From: Alexander Stein <alexander.stein@...tq-group.com>
To: Liu Ying <victor.liu@....com>, Marek Vasut <marex@...x.de>,
 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>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Francesco Valla <francesco@...la.it>
Cc: Fabian Pflug <f.pflug@...gutronix.de>, dri-devel@...ts.freedesktop.org,
 imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: ldb: add support for an external bridge

Hi Francesco,

Am Dienstag, 28. Oktober 2025, 13:12:29 CET schrieb Francesco Valla:
> One option for the LVDS port of the LDB is to be connected to an
> additional bridge, such as a LVDS to HDMI converter. Add support for
> such case, along with the direct connection to a panel.
> 
> Signed-off-by: Francesco Valla <francesco@...la.it>
> ---
> I was trying to add display support for the i.MX93 FRDM on top of the
> patch sent some time ago by Fabian Pflug [1], using some of the work
> already done by Alexander Stein but not yet merged [2], but then I
> noticed that the support for LVDS-HDMI converter bridges was missing
> from the LDB driver already present for the i.MX93.
> 
> Not a fail of the driver itself, obviously, but I wonder if/how the
> existing i.MX8MP setups (e.g.: [3]), which use the same driver, work
> correclty. Unfortunately I don't have the i.MX8MP hardware to test them.
> 
> Anyhow, a patch for such setup is attached; it was tested on the i.MX93
> FRDM using [1] and [2] plus some more devicetree modifications.
> 
> [1] https://lore.kernel.org/all/20251022-fpg-nxp-imx93-frdm-v3-1-03ec40a1ccc0@pengutronix.de
> [2] https://lore.kernel.org/all/20250304154929.1785200-1-alexander.stein@ew.tq-group.com
> [3] https://elixir.bootlin.com/linux/v6.17.5/source/arch/arm64/boot/dts/freescale/imx8mp-evk-lvds0-imx-dlvds-hdmi-channel0.dtso
> 
> Regards,
> Francesco
> ---
>  drivers/gpu/drm/bridge/fsl-ldb.c | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/fsl-ldb.c b/drivers/gpu/drm/bridge/fsl-ldb.c
> index 5c3cf37200bcee1db285c97e2b463c9355ee6acb..fad436f2e0bfac8b42096a6fcd0022da0f35284e 100644
> --- a/drivers/gpu/drm/bridge/fsl-ldb.c
> +++ b/drivers/gpu/drm/bridge/fsl-ldb.c
> @@ -294,7 +294,6 @@ 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;
>  
> @@ -335,15 +334,24 @@ static int fsl_ldb_probe(struct platform_device *pdev)
>  		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);
> -
> -	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);
> +	/* First try to get an additional bridge, if not found go for a panel */
> +	fsl_ldb->panel_bridge = of_drm_find_bridge(panel_node);
> +	if (fsl_ldb->panel_bridge) {
> +		of_node_put(panel_node);
> +	} else {
> +		struct drm_panel *panel;
>  
> +		panel = of_drm_find_panel(panel_node);
> +		of_node_put(panel_node);
> +		if (IS_ERR(panel))
> +			return dev_err_probe(dev, PTR_ERR(panel),
> +					     "Failed to find panel");
> +
> +		fsl_ldb->panel_bridge = devm_drm_panel_bridge_add(dev, panel);
> +		if (IS_ERR(fsl_ldb->panel_bridge))
> +			return dev_err_probe(dev, PTR_ERR(fsl_ldb->panel_bridge),
> +					     "Failed to add panel bridge");
> +	}

Without looking into the details this somehow looks similar to
drm_of_find_panel_or_bridge(), or drmm_of_get_bridge for the managed variant.

Best regards,
Alexander

>  
>  	if (fsl_ldb_is_dual(fsl_ldb)) {
>  		struct device_node *port1, *port2;
> 
> ---
> base-commit: fd57572253bc356330dbe5b233c2e1d8426c66fd
> change-id: 20251028-imx93_ldb_bridge-3c011e7856dc
> 
> Best regards,
> 


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