[PATCH] drm/imx: parallel-display: Prefer bus format set via legacy "interface-pix-fmt" DT property

[Marek Vasut]

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 at vger.kernel.org
Fixes: 5f6e56d3319d ("drm/imx: parallel-display: switch to drm_panel_bridge")
Signed-off-by: Marek Vasut <marex at nabladev.com>
---
Cc: David Airlie <airlied at gmail.com>
Cc: Fabio Estevam <festevam at gmail.com>
Cc: Pengutronix Kernel Team <kernel at pengutronix.de>
Cc: Philipp Zabel <p.zabel at pengutronix.de>
Cc: Sascha Hauer <s.hauer at pengutronix.de>
Cc: Shawn Guo <shawnguo at kernel.org>
Cc: Simona Vetter <simona at ffwll.ch>
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: dri-devel at lists.freedesktop.org
Cc: imx at lists.linux.dev
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-kernel at 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