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

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Message-ID: <1a52c081-ebb7-487b-850f-e50fb36b739a@nxp.com>
Date: Wed, 29 Oct 2025 11:41:51 +0800
From: Liu Ying <victor.liu@....com>
To: Francesco Valla <francesco@...la.it>, 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>
Cc: Alexander Stein <alexander.stein@...tq-group.com>,
 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

On 10/28/2025, Francesco Valla wrote:
> [You don't often get email from francesco@...la.it. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> 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.

[3] was in my previous patch series[a].  Only patch 6&7 of [a] are applied,
so for now [3] doesn't actually work with i.MX8MP.

And, patch 3 of [a] supports the external bridge this patch tries to support.

[b] is another patch series which includes my patch.

[a] https://patchwork.freedesktop.org/series/139266/#rev7
[b] https://patchwork.freedesktop.org/series/154381/

> 
> 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");
> +       }
> 
>         if (fsl_ldb_is_dual(fsl_ldb)) {
>                 struct device_node *port1, *port2;
> 
> ---
> base-commit: fd57572253bc356330dbe5b233c2e1d8426c66fd
> change-id: 20251028-imx93_ldb_bridge-3c011e7856dc
> 
> Best regards,
> --
> Francesco Valla <francesco@...la.it>
> 


-- 
Regards,
Liu Ying