Prefer bus format set via legacy "interface-pix-fmt" DT property
over panel bus format. This is necessary to retain support for
DTs which configure the IPUv3 parallel output as 24bit DPI, but
connect 18bit DPI panels to it with hardware swizzling.

This used to work up to Linux 6.12, but stopped working in 6.13,
reinstate the behavior to support old DTs.

Cc: stable@vger.kernel.org
Fixes: 5f6e56d3319d ("drm/imx: parallel-display: switch to drm_panel_bridge")
Signed-off-by: Marek Vasut <marex@nabladev.com>
---
Cc: David Airlie <airlied@gmail.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: dri-devel@lists.freedesktop.org
Cc: imx@lists.linux.dev
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/gpu/drm/imx/ipuv3/parallel-display.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/imx/ipuv3/parallel-display.c b/drivers/gpu/drm/imx/ipuv3/parallel-display.c
index 6fbf505d2801d..02bb38a1ee4eb 100644
--- a/drivers/gpu/drm/imx/ipuv3/parallel-display.c
+++ b/drivers/gpu/drm/imx/ipuv3/parallel-display.c
@@ -110,8 +110,7 @@ imx_pd_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
 		output_fmt = imxpd->bus_format ? : MEDIA_BUS_FMT_RGB888_1X24;
 
 	/* Now make sure the requested output format is supported. */
-	if ((imxpd->bus_format && imxpd->bus_format != output_fmt) ||
-	    !imx_pd_format_supported(output_fmt)) {
+	if (!imx_pd_format_supported(output_fmt)) {
 		*num_input_fmts = 0;
 		return NULL;
 	}
@@ -121,7 +120,17 @@ imx_pd_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
 	if (!input_fmts)
 		return NULL;
 
-	input_fmts[0] = output_fmt;
+	/*
+	 * Prefer bus format set via legacy "interface-pix-fmt" DT property
+	 * over panel bus format. This is necessary to retain support for
+	 * DTs which configure the IPUv3 parallel output as 24bit, but
+	 * connect 18bit DPI panels to it with hardware swizzling.
+	 */
+	if (imxpd->bus_format && imxpd->bus_format != output_fmt)
+		input_fmts[0] = imxpd->bus_format;
+	else
+		input_fmts[0] = output_fmt;
+
 	return input_fmts;
 }
 
-- 
2.51.0

On Sa, 2026-01-10 at 18:14 +0100, Marek Vasut wrote:
> Prefer bus format set via legacy "interface-pix-fmt" DT property
> over panel bus format. This is necessary to retain support for
> DTs which configure the IPUv3 parallel output as 24bit DPI, but
> connect 18bit DPI panels to it with hardware swizzling.
>
> This used to work up to Linux 6.12, but stopped working in 6.13,
> reinstate the behavior to support old DTs.
> 
> Cc: stable@vger.kernel.org
> Fixes: 5f6e56d3319d ("drm/imx: parallel-display: switch to drm_panel_bridge")
> Signed-off-by: Marek Vasut <marex@nabladev.com>

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>

regards
Philipp