linux-kernel - [PATCH v4 3/3] drm/bridge: microchip-lvds: fix bus format mismatch with VESA displays

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Message-ID: <20250624-microchip-lvds-v4-3-937d42a420e9@microchip.com>
Date: Tue, 24 Jun 2025 14:54:16 +0530
From: Dharma Balasubiramani <dharma.b@...rochip.com>
To: Manikandan Muralidharan <manikandan.m@...rochip.com>, 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>, David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
CC: <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>, "Dharma
 Balasubiramani" <dharma.b@...rochip.com>, Sandeep Sheriker M
	<sandeep.sheriker@...rochip.com>
Subject: [PATCH v4 3/3] drm/bridge: microchip-lvds: fix bus format mismatch
 with VESA displays

The LVDS controller was hardcoded to JEIDA mapping, which leads to
distorted output on panels expecting VESA mapping.

Update the driver to dynamically select the appropriate mapping and
pixel size based on the panel's advertised media bus format. This
ensures compatibility with both JEIDA and VESA displays.

Signed-off-by: Sandeep Sheriker M <sandeep.sheriker@...rochip.com>
Signed-off-by: Dharma Balasubiramani <dharma.b@...rochip.com>
---
 drivers/gpu/drm/bridge/microchip-lvds.c | 38 +++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/bridge/microchip-lvds.c b/drivers/gpu/drm/bridge/microchip-lvds.c
index e4ff46b03d54..ce52b794a9c6 100644
--- a/drivers/gpu/drm/bridge/microchip-lvds.c
+++ b/drivers/gpu/drm/bridge/microchip-lvds.c
@@ -11,6 +11,7 @@
 #include <linux/component.h>
 #include <linux/delay.h>
 #include <linux/jiffies.h>
+#include <linux/media-bus-format.h>
 #include <linux/mfd/syscon.h>
 #include <linux/of_graph.h>
 #include <linux/pinctrl/devinfo.h>
@@ -40,9 +41,11 @@
 
 /* Bitfields in LVDSC_CFGR (Configuration Register) */
 #define LVDSC_CFGR_PIXSIZE_24BITS	0
+#define LVDSC_CFGR_PIXSIZE_18BITS	BIT(0)
 #define LVDSC_CFGR_DEN_POL_HIGH		0
 #define LVDSC_CFGR_DC_UNBALANCED	0
 #define LVDSC_CFGR_MAPPING_JEIDA	BIT(6)
+#define LVDSC_CFGR_MAPPING_VESA		0
 
 /*Bitfields in LVDSC_SR */
 #define LVDSC_SR_CS	BIT(0)
@@ -74,9 +77,10 @@ static inline void lvds_writel(struct mchp_lvds *lvds, u32 offset, u32 val)
 	writel_relaxed(val, lvds->regs + offset);
 }
 
-static void lvds_serialiser_on(struct mchp_lvds *lvds)
+static void lvds_serialiser_on(struct mchp_lvds *lvds, u32 bus_format)
 {
 	unsigned long timeout = jiffies + msecs_to_jiffies(LVDS_POLL_TIMEOUT_MS);
+	u8 map, pix_size;
 
 	/* The LVDSC registers can only be written if WPEN is cleared */
 	lvds_writel(lvds, LVDSC_WPMR, (LVDSC_WPMR_WPKEY_PSSWD &
@@ -91,11 +95,24 @@ static void lvds_serialiser_on(struct mchp_lvds *lvds)
 		usleep_range(1000, 2000);
 	}
 
+	switch (bus_format) {
+	case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
+		map = LVDSC_CFGR_MAPPING_JEIDA;
+		pix_size = LVDSC_CFGR_PIXSIZE_18BITS;
+		break;
+	case MEDIA_BUS_FMT_RGB888_1X7X4_SPWG:
+		map = LVDSC_CFGR_MAPPING_VESA;
+		pix_size = LVDSC_CFGR_PIXSIZE_24BITS;
+		break;
+	default:
+		map = LVDSC_CFGR_MAPPING_JEIDA;
+		pix_size = LVDSC_CFGR_PIXSIZE_24BITS;
+		break;
+	}
+
 	/* Configure the LVDSC */
-	lvds_writel(lvds, LVDSC_CFGR, (LVDSC_CFGR_MAPPING_JEIDA |
-				LVDSC_CFGR_DC_UNBALANCED |
-				LVDSC_CFGR_DEN_POL_HIGH |
-				LVDSC_CFGR_PIXSIZE_24BITS));
+	lvds_writel(lvds, LVDSC_CFGR, map | LVDSC_CFGR_DC_UNBALANCED |
+		    LVDSC_CFGR_DEN_POL_HIGH | pix_size);
 
 	/* Enable the LVDS serializer */
 	lvds_writel(lvds, LVDSC_CR, LVDSC_CR_SER_EN);
@@ -134,7 +151,16 @@ static void mchp_lvds_atomic_enable(struct drm_bridge *bridge,
 				    struct drm_atomic_state *state)
 {
 	struct mchp_lvds *lvds = bridge_to_lvds(bridge);
-	lvds_serialiser_on(lvds);
+	struct drm_connector *connector;
+
+	/* default to jeida-24 */
+	u32 bus_format = MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA;
+
+	connector = drm_atomic_get_new_connector_for_encoder(state, bridge->encoder);
+	if (connector && connector->display_info.num_bus_formats)
+		bus_format = connector->display_info.bus_formats[0];
+
+	lvds_serialiser_on(lvds, bus_format);
 }
 
 static void mchp_lvds_atomic_disable(struct drm_bridge *bridge,

-- 
2.43.0