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.

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]/
Link to v4: https://lore.kernel.org/all/[email protected]/
Link to v5: https://lore.kernel.org/all/[email protected]/
---
Changes in v6:

Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml:
- Drop Assisted-by tag.
- Remove sentence referencing driver polling from interrupt description.

drivers/gpu/drm/tiny/ra8875.c:
- use drm_atomic_helper_connector_create_state instead of drm_atomic_helper_connector_reset.

Changes in v5:

Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml:
- Drop the "Add YAML binding schema..." paragraph from the commit message (Krzysztof)
- Add interrupts property for the INT# pin

drivers/gpu/drm/tiny/ra8875.c:
- Move bindings table to above ra8875_spi_driver definition

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   |  86 +++
 .../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, 827 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.

---
 .../bindings/display/panel/raio,ra8875.yaml   | 86 +++++++++++++++++++
 .../devicetree/bindings/vendor-prefixes.yaml  |  2 +
 2 files changed, 88 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml

new file mode 100644
index 000000000000..4c72130f0dbe
@@ -0,0 +1,86 @@
+# 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 host 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
+
+  interrupts:
+    description:
+      INT# pin, active low. Signals RA8875 interrupt events such as touch
+      panel, key scan, DMA, BTE and font access completion.
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - display-timings
+  - vdd-supply
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.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>;
+            interrupt-parent = <&gpio>;
+            interrupts = <5 IRQ_TYPE_LEVEL_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 7602034374d7..c834ad2eb582 100644
@@ -1411,6 +1411,8 @@ patternProperties:
     description: Radxa
   "^raidsonic,.*":
     description: RaidSonic Technology GmbH
+  "^raio,.*":
+    description: RAiO Technology Inc.
   "^ralink,.*":
     description: Mediatek/Ralink Technology Corp.
   "^ramtron,.*":

2.55.0

Best regards,
Krzysztof

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 2e6bca640901..70d194ad0f37 100644
@@ -8648,6 +8648,12 @@ 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