drm/tiny: Add RAiO RA8875 display controller driver support

This series adds a new drm/tiny driver and matching dt-binding for the RAiO RA8875 SPI display controller. An fbtft driver for this chip currently exists at drivers/staging/fbtft/fb_ra8875.c, but fbtft is a legacy fbdev-based staging driver, and nothing in mainline DRM currently supports this controller.

This driver does not use drm_mipi_dbi. The RA8875 SPI protocol is structurally incompatible with both Type C options drm_mipi_dbi supports. Type C1 encodes command/data as a 9th bit within a 9-bit SPI word. The RA8875 uses a full prefix byte (0x80 = command write, 0x00 = data write, 0x40 = data read, 0xC0 = status read) sent as a separate 8-bit transaction. These are not the same thing and cannot be mapped to each other. Type C3 models two transfer types via a D/CX GPIO. The RA8875 has four transfer cycle types and no D/CX pin.

My ER-TFTM050-3 board has RST tied NC, and VDD is a fixed supply set via an on-board solder jumper rather than software-controllable, so I couldn't test reset-gpios/vdd-supply myself, but added them as optional/required properties respectively per review feedback for boards that do need them.

Tested on a Raspberry Pi 3B connected over SPI to an East Rising ER-TFTM050-3, a 5" 800x480 panel driven by the RA8875 in Linux 7.3.0-rc4. Based on drm-misc-next (commit 73df79cceb8c)

Link to v1: https://lore.kernel.org/all/[email protected]/
Link to v2: https://lore.kernel.org/all/[email protected]/
Link to v3: https://lore.kernel.org/all/[email protected]/
---
Changes in v4:

Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml:
- Drop the sentence in the description saying the binding covers only the SPI-connected device (Conor).
- Drop unused panel label

drivers/gpu/drm/tiny/ra8875.c:
- Catch error value from ra8875_write_pixels
- Use consistent include header format.
- Return if fb is null in atomic_update
- Drop unnecessary extra byte in pixel data spi write.

drivers/gpu/drm/tiny/Kconfig:
- Add depends on OF, which is caught by intel 0-day[3]

Changes in v3:

Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml:
- Add gpio.h include in example to pass dt_binding_check
- Remove spi-max-frequency as there is no reference in datasheet

drivers/gpu/drm/tiny/ra8875.c:
- Remove debug-only ra8875_read_reg function
- Chunk large SPI transfers to 16 rows per chunk
- Remove unnecessary includes and spi cs setups in probe
- Create ra8875_write_pixels function for clear_screen and fb_dirty
- Use 2 spi writes instead of 1 write with 2 transfers and cs_change in write_reg

Changes in v2:

Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml (review by Krzysztof Kozlowski):
- Add hardware description to the binding
- Drop the display-timings property, and instead require it in the required block
- Add a required vdd-supply and an optional reset gpio property
- Rename the example node to a more generic "panel: display@0"

drivers/gpu/drm/tiny/Makefile and Kconfig:
- Remove TINYDRM prefix from the config name (Thomas Zimmermann [1])

drivers/gpu/drm/tiny/ra8875.c:
- Reformat device_id table to match current convention (Krzysztof Kozlowski)
- Drop unneeded linux/mod_devicetable.h include (Uwe Kleine-König)
- Use drm_dev_unplug() instead of drm_dev_unregister() in remove callback
- Move stack-allocated cmd/data buffers into ra8875_device struct
- Add mode_valid() callback to validate height/width against panel maximum
- Add optional reset gpio
- Use dev_err_probe() in probe function
- Remove connector detect callback
- Remove unnecessary |= on register write return value in hw_init
- Migrate from simple display pipe to manually-handled plane/crtc/encoder, following the simple-KMS-helper removal effort [2]
- Use defined constants instead of magic values where possible
- Use drm_atomic_helper_damage_merged() and drm_fb_swab() in plane update

[1] https://lore.kernel.org/all/[email protected]/
[2] https://lore.kernel.org/all/20260705-drm-simple-kms-removal-v1-0-b4e1ca053623@oss.qualcomm.com/
[3] https://lore.kernel.org/all/[email protected]/

Adam Azuddin (2):
dt-bindings: display: panel: Add RAiO RA8875 display controller drm/tiny: Add RAiO RA8875 display controller driver

 .../bindings/display/panel/raio,ra8875.yaml   |  77 ++
 .../devicetree/bindings/vendor-prefixes.yaml  |   2 +
 MAINTAINERS                                   |   6 +
 drivers/gpu/drm/tiny/Kconfig                  |  13 +
 drivers/gpu/drm/tiny/Makefile                 |   1 +
 drivers/gpu/drm/tiny/ra8875.c                 | 719 ++++++++++++++++++
 6 files changed, 818 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml
 create mode 100644 drivers/gpu/drm/tiny/ra8875.c

2.55.0

The RA8875 is an SPI-connected TFT display controller by RAiO Technology Inc. It supports display resolutions of up to 800x480.

Add YAML binding schema for the RA8875 controller, along with the raio vendor prefix for RAiO Technology Inc.

---
 .../bindings/display/panel/raio,ra8875.yaml   | 77 +++++++++++++++++++
 .../devicetree/bindings/vendor-prefixes.yaml  |  2 +
 2 files changed, 79 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml

new file mode 100644
index 000000000000..86777e2cec57
@@ -0,0 +1,77 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/raio,ra8875.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: RAiO RA8875 Display Controller
+
+maintainers:
+  - Adam Azuddin <[email protected]>
+
+description:
+  The RA8875 is a TFT LCD controller for panels up to 800x480 pixels.
+  It can be connected to the controller via 8080/6800 parallel interface,
+  SPI or I2C.
+
+allOf:
+  - $ref: panel-common.yaml#
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    const: raio,ra8875
+
+  reg:
+    maxItems: 1
+
+  vdd-supply:
+    description:
+      3.3 V supply for the IO pins, the oscillator IO pins, the ADC pins
+      and the internal LDO. The 1.8 V core rail is generated internally.
+
+  reset-gpios:
+    description:
+      GPIO connected to the active-low RST# pin. Optional, since the board
+      may instead use an RC reset circuit.
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - display-timings
+  - vdd-supply
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        display@0 {
+            compatible = "raio,ra8875";
+            reg = <0>;
+            spi-max-frequency = <16000000>;
+            vdd-supply = <&vcc_3v3>;
+            reset-gpios = <&gpio 25 GPIO_ACTIVE_LOW>;
+
+            display-timings {
+                native-mode = <&timing0>;
+                timing0: timing0 {
+                    clock-frequency = <25000000>;
+                    hactive = <800>;
+                    vactive = <480>;
+                    hfront-porch = <40>;
+                    hsync-len = <40>;
+                    hback-porch = <40>;
+                    vfront-porch = <10>;
+                    vsync-len = <10>;
+                    vback-porch = <20>;
+                };
+            };
+        };
+    };

index ba2002969373..99d5113fb035 100644
@@ -1395,6 +1395,8 @@ patternProperties:
     description: Radxa
   "^raidsonic,.*":
     description: RaidSonic Technology GmbH
+  "^raio,.*":
+    description: RAiO Technology Inc.
   "^ralink,.*":
     description: Mediatek/Ralink Technology Corp.
   "^ramtron,.*":

2.55.0

So you ignored my feedback.

Not reviewing the rest.

Best regards,
Krzysztof

Hi Krzysztof,

My mistake, I misunderstood your feedback regarding the redundant binding text in the commit description.

I will fix the commit message and send v5.

Best regards,
Adam

Add a DRM tiny driver for the RAiO RA8875 SPI-connected TFT display controller. The driver supports display resolutions up to 800x480 and uses the GEM shmem helper for buffer management.

---
 MAINTAINERS                   |   6 +
 drivers/gpu/drm/tiny/Kconfig  |  13 +
 drivers/gpu/drm/tiny/Makefile |   1 +
 drivers/gpu/drm/tiny/ra8875.c | 719 ++++++++++++++++++++++++++++++++++
 4 files changed, 739 insertions(+)
 create mode 100644 drivers/gpu/drm/tiny/ra8875.c

index a08087fb6e67..ccc36f168e19 100644
@@ -8450,6 +8450,12 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
 F:	drivers/gpu/drm/qxl/
 F:	include/uapi/drm/qxl_drm.h
 
+DRM DRIVER FOR RAIO RA8875 PANELS
+M:	Adam Azuddin <[email protected]>
+S:	Maintained
+F:	Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml
+F:	drivers/gpu/drm/tiny/ra8875.c
+
 DRM DRIVER FOR RAYDIUM RM67191 PANELS
 M:	Robert Chiras <[email protected]>
 S:	Maintained

index f0e72d4b6a47..2f1c49e31dd6 100644
@@ -98,6 +98,19 @@ config DRM_PIXPAPER
 
 	  If M is selected, the module will be built as pixpaper.ko.
 
+config DRM_RA8875
+	tristate "DRM support for RA8875 display panels"
+	depends on DRM && SPI && OF
+	select DRM_CLIENT_SELECTION
+	select DRM_KMS_HELPER
+	select DRM_GEM_SHMEM_HELPER
+	select VIDEOMODE_HELPERS
+	help
+	  DRM driver for the following RAiO RA8875 based LCD panels:
+	  * East Rising 5.00" TFT LCD (ER-TFTM050-3)
+
+	  If M is selected the module will be called ra8875.
+
 config TINYDRM_HX8357D
 	tristate "DRM support for HX8357D display panels"
 	depends on DRM && SPI

index 48d30bf6152f..ed4602097fbb 100644
@@ -14,4 +14,5 @@ obj-$(CONFIG_TINYDRM_ILI9341)		+= ili9341.o
 obj-$(CONFIG_TINYDRM_ILI9486)		+= ili9486.o
 obj-$(CONFIG_TINYDRM_MI0283QT)		+= mi0283qt.o
 obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
+obj-$(CONFIG_DRM_RA8875)		+= ra8875.o
 obj-$(CONFIG_TINYDRM_SHARP_MEMORY)	+= sharp-memory.o

2.55.0