drm/panel: simple: add bus-format support for panel-dpi

From: Max Krummenacher <[email protected]>

Commit 4a1d0dbc8332 ("drm/panel: simple: add panel-dpi support") added support for defining a panel from device tree provided data.

However support for setting the bus format is missing, so that with the current implementation a 'panel-dpi' panel can only be used if the driver of the display interface connected can cope with a missing bus_format.

This patch series defines the new property bus-format and adds it to the panel-dpi implementation.

Check initial discussions [1] and [2].
[1] https://lore.kernel.org/all/[email protected]/
[2] https://lore.kernel.org/all/[email protected]/

Max Krummenacher (2):
dt-bindings: display: add new bus-format property for panel-dpi drm/panel: simple: add bus-format support for panel-dpi

 .../bindings/display/panel/panel-dpi.yaml     | 11 +++++
 drivers/gpu/drm/panel/panel-simple.c          | 43 +++++++++++++++++++
 .../dt-bindings/display/dt-media-bus-format.h | 23 ++++++++++
 3 files changed, 77 insertions(+)
 create mode 100644 include/dt-bindings/display/dt-media-bus-format.h

2.20.1

From: Max Krummenacher <[email protected]>

The property is used to set the enum bus_format and infer the bpc for a panel defined by 'panel-dpi'.
This specifies how the panel is connected to the display interface.

---

 .../bindings/display/panel/panel-dpi.yaml     | 11 +++++++++
 .../dt-bindings/display/dt-media-bus-format.h | 23 +++++++++++++++++++
 2 files changed, 34 insertions(+)
 create mode 100644 include/dt-bindings/display/dt-media-bus-format.h

index dae0676b5c6e..ca44e96c3001 100644
@@ -21,6 +21,14 @@ properties:
       - {}
       - const: panel-dpi
 
+  bus-format:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: |
+      Describes how the display panel is connected to the display interface.
+      Valid values are defined in <dt-bindings/display/dt-media-bus-format.h>.
+      The mapping between the color/significance of the panel lines to the
+      parallel data lines are defined in [1].
+      [1] https://www.kernel.org/doc/html/v5.17/userspace-api/media/v4l/subdev-formats.html#packed-rgb-formats
   backlight: true
   enable-gpios: true
   height-mm: true

@@ -39,11 +47,14 @@ additionalProperties: false
 
 examples:
   - |
+    #include <dt-bindings/display/dt-media-bus-format.h>
+    ...
     panel {
         compatible = "startek,startek-kd050c", "panel-dpi";
         label = "osddisplay";
         power-supply = <&vcc_supply>;
         backlight = <&backlight>;
+        bus-format = "DT_MEDIA_BUS_FMT_RGB888_1X24";
 
         port {
             lcd_in: endpoint {

new file mode 100644
index 000000000000..c0f2a7b59aa1
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only OR MIT */
+/*
+ * Copyright 2022 Max Krummenacher <[email protected]>
+ */
+
+#ifndef __DT_BINDINGS_DT_MEDIA_BUS_FORMAT_H
+#define __DT_BINDINGS_DT_MEDIA_BUS_FORMAT_H
+
+/*
+ * Attention: Keep these macro names in sync with
+ * include/uapi/linux/media-bus-format.h
+ */
+
+#define DT_MEDIA_BUS_FMT_RGB565_1X16		1
+#define DT_MEDIA_BUS_FMT_RGB666_1X18		2
+#define DT_MEDIA_BUS_FMT_RBG888_1X24		3
+#define DT_MEDIA_BUS_FMT_RGB666_1X24_CPADHI	4
+#define DT_MEDIA_BUS_FMT_BGR888_1X24		5
+#define DT_MEDIA_BUS_FMT_GBR888_1X24		6
+#define DT_MEDIA_BUS_FMT_RGB888_1X24		7
+#define DT_MEDIA_BUS_FMT_RGB888_1X32_PADHI	8
+
+#endif /* __DT_BINDINGS_DT_MEDIA_BUS_FORMAT_H */

2.20.1

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check' on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
Error: Documentation/devicetree/bindings/display/panel/panel-dpi.example.dts:20.9-10 syntax error FATAL ERROR: Unable to parse input tree
make[1]: *** [scripts/Makefile.lib:364: Documentation/devicetree/bindings/display/panel/panel-dpi.example.dtb] Error 1 make[1]: *** Waiting for unfinished jobs....
make: *** [Makefile:1401: dt_binding_check] Error 2

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/patch/

This check can fail if there are any dependencies. The base for a patch series is generally the most recent rc1.

If you already ran 'make dt_binding_check' and didn't see the above error(s), then make sure 'yamllint' is installed and dt-schema is up to date:

pip3 install dtschema --upgrade

Please check and re-submit.

From: Max Krummenacher <[email protected]>

Evaluate the device tree bus-format property to set bus_format for a 'panel-dpi' panel. Additionally infer the bpc value from the given bus-format.

Valid values for bus-format are found in:
<include/dt-bindings/display/dt-media-bus-format.h>

This completes the addition of panel-dpi to completely specify a panel-simple panel from the device tree.

---

 drivers/gpu/drm/panel/panel-simple.c | 43 ++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

index a34f4198a534..090c60abb014 100644
@@ -21,6 +21,7 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#include <dt-bindings/display/dt-media-bus-format.h>
 #include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/module.h>

@@ -453,6 +454,7 @@ static int panel_dpi_probe(struct device *dev,
 	struct panel_desc *desc;
 	unsigned int bus_flags;
 	struct videomode vm;
+	u32 bus_format;
 	int ret;
 
 	np = dev->of_node;

@@ -477,6 +479,47 @@ static int panel_dpi_probe(struct device *dev,
 	of_property_read_u32(np, "width-mm", &desc->size.width);
 	of_property_read_u32(np, "height-mm", &desc->size.height);
 
+	if (!of_property_read_u32(np, "bus-format", &bus_format)) {
+		/* infer bpc from bus-format */
+		switch (bus_format) {
+		case DT_MEDIA_BUS_FMT_RGB565_1X16:
+			desc->bus_format = MEDIA_BUS_FMT_RGB565_1X16;
+			desc->bpc = 6;
+			break;
+		case DT_MEDIA_BUS_FMT_RGB666_1X18:
+			desc->bus_format = MEDIA_BUS_FMT_RGB666_1X18;
+			desc->bpc = 6;
+			break;
+		case DT_MEDIA_BUS_FMT_RGB666_1X24_CPADHI:
+			desc->bus_format = MEDIA_BUS_FMT_RGB666_1X24_CPADHI;
+			desc->bpc = 6;
+			break;
+		case DT_MEDIA_BUS_FMT_BGR888_1X24:
+			desc->bus_format = MEDIA_BUS_FMT_BGR888_1X24;
+			desc->bpc = 8;
+			break;
+		case DT_MEDIA_BUS_FMT_GBR888_1X24:
+			desc->bus_format = MEDIA_BUS_FMT_GBR888_1X24;
+			desc->bpc = 8;
+			break;
+		case DT_MEDIA_BUS_FMT_RBG888_1X24:
+			desc->bus_format = MEDIA_BUS_FMT_RBG888_1X24;
+			desc->bpc = 8;
+			break;
+		case DT_MEDIA_BUS_FMT_RGB888_1X24:
+			desc->bus_format = MEDIA_BUS_FMT_RGB888_1X24;
+			desc->bpc = 8;
+			break;
+		case DT_MEDIA_BUS_FMT_RGB888_1X32_PADHI:
+			desc->bus_format = MEDIA_BUS_FMT_RGB888_1X32_PADHI;
+			desc->bpc = 8;
+			break;
+		default:
+			dev_err(dev, "%pOF: unknown bus-format property\n", np);
+			return -EINVAL;
+		}
+	}
+
 	/* Extract bus_flags from display_timing */
 	bus_flags = 0;
 	vm.flags = timing->flags;

2.20.1