[PATCH v4 0/4] drm: mxsfb: Support LCDIF interface bus width

[PATCH v4 0/4] drm: mxsfb: Support LCDIF interface bus width

[Francesco Dolcini]

From: Francesco Dolcini <francesco.dolcini@toradex.com>

The width of the physical LCDIF output bus can differ from the input bus
format advertised by the downstream panel or bridge.

Such a distinction is required when the LCDIF bus width does not match the
width of the downstream display interface. For example, an 18-bit or
16-bit LCDIF bus can drive a 24-bit display by wiring the available color
bits to the appropriate display inputs. Configuring LCDIF solely from the
display's 24-bit format in this case selects the wrong LCD_DATABUS_WIDTH
mode, changing the color-bit assignment on the LCD_DATA pins and resulting
in incorrect colors.

Use the common OF graph endpoint bus-width property to describe the width
of the physical LCDIF output bus. Make the mxsfb driver derive the
corresponding media bus format from this property and use it in preference
to the format reported by the downstream display. When the property is
absent, the existing behavior is preserved.

Set the endpoint bus width for the Colibri iMX6ULL and Colibri iMX7 boards,
which route an 18-bit LCD interface.

v4:
 - use /schemas/graph.yaml#/$defs/port-base
 - add r-b and t-b tags
v3: https://lore.kernel.org/all/20260812132954.148571-1-francesco@dolcini.it/
 - use video-interfaces.yaml
v2: https://lore.kernel.org/all/20260723093813.180089-1-francesco@dolcini.it/
 - use the common bus-width property instead of the legacy interface-pix-fmt
v1: https://lore.kernel.org/all/20260717121847.488148-1-francesco@dolcini.it/

Francesco Dolcini (4):
  dt-bindings: lcdif: Add endpoint bus-width property
  drm: mxsfb: Add optional DPI output bus-width configuration
  ARM: dts: imx6ull-colibri: Set LCDIF bus-width
  ARM: dts: imx7-colibri: Set LCDIF bus-width

 .../bindings/display/fsl,lcdif.yaml           | 12 +++++++++-
 .../arm/boot/dts/nxp/imx/imx6ull-colibri.dtsi |  1 +
 arch/arm/boot/dts/nxp/imx/imx7-colibri.dtsi   |  1 +
 drivers/gpu/drm/mxsfb/mxsfb_drv.c             | 24 +++++++++++++++++++
 drivers/gpu/drm/mxsfb/mxsfb_drv.h             |  2 ++
 drivers/gpu/drm/mxsfb/mxsfb_kms.c             | 12 ++++++++++
 6 files changed, 51 insertions(+), 1 deletion(-)

-- 
2.47.3

[PATCH v4 1/4] dt-bindings: lcdif: Add endpoint bus-width property

[Francesco Dolcini]

From: Francesco Dolcini <francesco.dolcini@toradex.com>

The DPI output of the LCD interface can be configured with a bus width
of 16, 18, or 24 bits. Introduce a bus-width property to the output
endpoint, specifying the number of parallel RGB bits connected.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
v4: use /schemas/graph.yaml#/$defs/port-base
v3: use video-interfaces.yaml
v2: use the common bus-width property instead of the legacy interface-pix-fmt
---
 .../devicetree/bindings/display/fsl,lcdif.yaml       | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/display/fsl,lcdif.yaml b/Documentation/devicetree/bindings/display/fsl,lcdif.yaml
index 2dd0411ec651..89cea0c14cf1 100644
--- a/Documentation/devicetree/bindings/display/fsl,lcdif.yaml
+++ b/Documentation/devicetree/bindings/display/fsl,lcdif.yaml
@@ -68,9 +68,19 @@ properties:
     maxItems: 1
 
   port:
-    $ref: /schemas/graph.yaml#/properties/port
+    $ref: /schemas/graph.yaml#/$defs/port-base
+    unevaluatedProperties: false
     description: The LCDIF output port
 
+    properties:
+      endpoint:
+        $ref: /schemas/media/video-interfaces.yaml
+        unevaluatedProperties: false
+
+        properties:
+          bus-width:
+            enum: [ 16, 18, 24 ]
+
   display:
     $ref: /schemas/types.yaml#/definitions/phandle
     description: phandle to display panel
-- 
2.47.3

Re: [PATCH v4 1/4] dt-bindings: lcdif: Add endpoint bus-width property

[Alexander Stein]

Am Donnerstag, 13. August 2026, 11:28:31 CEST schrieb Francesco Dolcini:
> From: Francesco Dolcini <francesco.dolcini@toradex.com>
> 
> The DPI output of the LCD interface can be configured with a bus width
> of 16, 18, or 24 bits. Introduce a bus-width property to the output
> endpoint, specifying the number of parallel RGB bits connected.
> 
> Reviewed-by: Frank Li <Frank.Li@nxp.com>
> Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>

Acked-by: Alexander Stein <alexander.stein@ew.tq-group.com>

> ---
> v4: use /schemas/graph.yaml#/$defs/port-base
> v3: use video-interfaces.yaml
> v2: use the common bus-width property instead of the legacy interface-pix-fmt
> ---
>  .../devicetree/bindings/display/fsl,lcdif.yaml       | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/display/fsl,lcdif.yaml b/Documentation/devicetree/bindings/display/fsl,lcdif.yaml
> index 2dd0411ec651..89cea0c14cf1 100644
> --- a/Documentation/devicetree/bindings/display/fsl,lcdif.yaml
> +++ b/Documentation/devicetree/bindings/display/fsl,lcdif.yaml
> @@ -68,9 +68,19 @@ properties:
>      maxItems: 1
>  
>    port:
> -    $ref: /schemas/graph.yaml#/properties/port
> +    $ref: /schemas/graph.yaml#/$defs/port-base
> +    unevaluatedProperties: false
>      description: The LCDIF output port
>  
> +    properties:
> +      endpoint:
> +        $ref: /schemas/media/video-interfaces.yaml
> +        unevaluatedProperties: false
> +
> +        properties:
> +          bus-width:
> +            enum: [ 16, 18, 24 ]
> +
>    display:
>      $ref: /schemas/types.yaml#/definitions/phandle
>      description: phandle to display panel
> 


-- 
TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
Amtsgericht München, HRB 105018
Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
http://www.tq-group.com/

[PATCH v4 2/4] drm: mxsfb: Add optional DPI output bus-width configuration

[Francesco Dolcini]

From: Francesco Dolcini <francesco.dolcini@toradex.com>

LCDIF programs LCD_DATABUS_WIDTH from the selected media bus format. The
format reported by the downstream panel or bridge describes the display
input, but it does not describe how the LCDIF data pins are physically
wired on the board.

These can differ. For example, a 16-bit LCDIF bus can be connected to a
24-bit display by wiring the available color bits to the corresponding
display inputs. In that case, using the display's 24-bit format to
configure LCDIF selects the wrong data-bus mode and changes the assignment
of color bits on the LCD_DATA pins.

Read the optional bus-width endpoint property from the LCDIF output port
and use it to select the media bus format used to configure LCDIF. This
allows the LCDIF bus mode to describe the physical interface
independently of the downstream display format.

When the optional property is absent, or it has an invalid value, continue
using the format reported by the downstream display device, preserving
the existing behavior. The code is not validating the DT for
correctness and just fall back to the previous behavior in case of
errors.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com> # TQMa6UL[L]x
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
v4: add r-b and t-b tags
v3: improve commit message and make it clear that the code assumes that
    the DT is correct, when the DT contains an invalid property value,
    the code safely fall-back to the previous behavior
v2: use the common bus-width property instead of the legacy interface-pix-fmt
---
 drivers/gpu/drm/mxsfb/mxsfb_drv.c | 24 ++++++++++++++++++++++++
 drivers/gpu/drm/mxsfb/mxsfb_drv.h |  2 ++
 drivers/gpu/drm/mxsfb/mxsfb_kms.c | 12 ++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
index 8b4a500347fb..f8ecc8bbd63c 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
@@ -12,7 +12,10 @@
 #include <linux/clk.h>
 #include <linux/dma-mapping.h>
 #include <linux/io.h>
+#include <linux/media-bus-format.h>
 #include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_graph.h>
 #include <linux/platform_device.h>
 #include <linux/property.h>
 #include <linux/pm_runtime.h>
@@ -211,7 +214,10 @@ static int mxsfb_load(struct drm_device *drm,
 		      const struct mxsfb_devdata *devdata)
 {
 	struct platform_device *pdev = to_platform_device(drm->dev);
+	struct device_node *np = pdev->dev.of_node;
 	struct mxsfb_drm_private *mxsfb;
+	struct device_node *ep;
+	u32 bus_width = 0;
 	int ret;
 
 	mxsfb = devm_kzalloc(&pdev->dev, sizeof(*mxsfb), GFP_KERNEL);
@@ -238,6 +244,24 @@ static int mxsfb_load(struct drm_device *drm,
 	if (IS_ERR(mxsfb->clk_disp_axi))
 		mxsfb->clk_disp_axi = NULL;
 
+	ep = of_graph_get_next_endpoint(np, NULL);
+	if (ep) {
+		of_property_read_u32(ep, "bus-width", &bus_width);
+		of_node_put(ep);
+	}
+
+	switch (bus_width) {
+	case 16:
+		mxsfb->bus_format = MEDIA_BUS_FMT_RGB565_1X16;
+		break;
+	case 18:
+		mxsfb->bus_format = MEDIA_BUS_FMT_RGB666_1X18;
+		break;
+	case 24:
+		mxsfb->bus_format = MEDIA_BUS_FMT_RGB888_1X24;
+		break;
+	}
+
 	ret = dma_set_mask_and_coherent(drm->dev, DMA_BIT_MASK(32));
 	if (ret)
 		return ret;
diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.h b/drivers/gpu/drm/mxsfb/mxsfb_drv.h
index d160d921b25f..bdc47ce5be79 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_drv.h
+++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.h
@@ -46,6 +46,8 @@ struct mxsfb_drm_private {
 	struct drm_connector		*connector;
 	struct drm_bridge		*bridge;
 
+	u32				bus_format;
+
 	bool				crc_active;
 };
 
diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
index d8ebebc5314b..1d78c486d147 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
@@ -386,6 +386,18 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
 	if (!bus_format)
 		bus_format = MEDIA_BUS_FMT_RGB888_1X24;
 
+	/*
+	 * Prefer the bus format derived from the OF graph endpoint "bus-width"
+	 * property when available. Otherwise, use the bus format reported by
+	 * the downstream bridge or panel.
+	 *
+	 * This supports mismatched display and interface bus widths, such as
+	 * a 24-bit panel connected through an 18-bit interface or an 18-bit
+	 * panel connected through a 24-bit interface.
+	 */
+	if (mxsfb->bus_format)
+		bus_format = mxsfb->bus_format;
+
 	mxsfb_crtc_mode_set_nofb(mxsfb, bridge_state, bus_format);
 
 	/* Write cur_buf as well to avoid an initial corrupt frame */
-- 
2.47.3

[PATCH v4 3/4] ARM: dts: imx6ull-colibri: Set LCDIF bus-width

[Francesco Dolcini]

From: Francesco Dolcini <francesco.dolcini@toradex.com>

The lcd DPI interface on colibri imx6ull uses a 18-bit width bus, set
the bus-width property accordingly.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
v4: no changes
v3: no changes
v2: use the common bus-width property instead of the legacy interface-pix-fmt
---
 arch/arm/boot/dts/nxp/imx/imx6ull-colibri.dtsi | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/boot/dts/nxp/imx/imx6ull-colibri.dtsi b/arch/arm/boot/dts/nxp/imx/imx6ull-colibri.dtsi
index ec3c1e7301f4..1eb1cf2d7395 100644
--- a/arch/arm/boot/dts/nxp/imx/imx6ull-colibri.dtsi
+++ b/arch/arm/boot/dts/nxp/imx/imx6ull-colibri.dtsi
@@ -229,6 +229,7 @@ &lcdif {
 
 	port {
 		lcdif_out: endpoint {
+			bus-width = <18>;
 			remote-endpoint = <&lcd_panel_in>;
 		};
 	};
-- 
2.47.3

[PATCH v4 4/4] ARM: dts: imx7-colibri: Set LCDIF bus-width

[Francesco Dolcini]

From: Francesco Dolcini <francesco.dolcini@toradex.com>

The lcd DPI interface on colibri imx7 uses a 18-bit width bus, set
the bus-width property accordingly.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
v4: no changes
v3: no changes
v2: use the common bus-width property instead of the legacy interface-pix-fmt
---
 arch/arm/boot/dts/nxp/imx/imx7-colibri.dtsi | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/boot/dts/nxp/imx/imx7-colibri.dtsi b/arch/arm/boot/dts/nxp/imx/imx7-colibri.dtsi
index 8666dcd7fe97..c4088d3c5ab1 100644
--- a/arch/arm/boot/dts/nxp/imx/imx7-colibri.dtsi
+++ b/arch/arm/boot/dts/nxp/imx/imx7-colibri.dtsi
@@ -537,6 +537,7 @@ &lcdif {
 
 	port {
 		lcdif_out: endpoint {
+			bus-width = <18>;
 			remote-endpoint = <&lcd_panel_in>;
 		};
 	};
-- 
2.47.3