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. More critically, the GRAM write path is stateful: an MRWC register-address transaction followed by a streaming pixel pump under a single CS assertion. I thought this may be too complicated to cater towards, but please let me know if this is the correct approach.

My ER-TFTM050-3 board has RST tied NC, and VDD is a fixed supply
set via an on-board solder jumper (3.3V/5V) rather than software-controllable, so reset-gpios/vcc-supply are not implemented in either the driver or the binding. I can add both as optional properties in v2 if reviewers know of RA8875 boards that do need this.

Tested on a Raspberry Pi 3B connected over SPI to an East Rising ER-TFTM050-3, a 5" 800x480 panel driven by the RA8875.

Ran fbtest (https://git.kernel.org/pub/scm/linux/kernel/git/geert/fbtest.git) against the resulting framebuffer:
./fbtest -f /dev/fb1
Using drawops cfb16 (16 bpp packed pixels)
Available visuals:

    Monochrome
    Grayscale 32
    Truecolor 5:6:5:0

Using visops truecolor
Running all tests
test001: PASSED
test002: PASSED
test003: PASSED
test004: PASSED
test005: PASSED
test006: PASSED
test008: PASSED
test009: PASSED
test010: PASSED
Benchmarking... 10x10 squares: 74.24 Mpixels/s Benchmarking... 20x20 squares: 152.49 Mpixels/s Benchmarking... 50x50 squares: 334.09 Mpixels/s Benchmarking... 100x100 squares: 591.46 Mpixels/s Benchmarking... 200x200 squares: 999.49 Mpixels/s
test012: PASSED
Benchmarking... R5 circles: 45.90 Mpixels/s Benchmarking... R10 circles: 98.84 Mpixels/s Benchmarking... R25 circles: 236.37 Mpixels/s Benchmarking... R50 circles: 459.98 Mpixels/s Benchmarking... R100 circles: 851.43 Mpixels/s
test013: PASSED

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   |  66 ++
 .../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                 | 739 ++++++++++++++++++
 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.

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

---
 .../bindings/display/panel/raio,ra8875.yaml   | 66 +++++++++++++++++++
 .../devicetree/bindings/vendor-prefixes.yaml  |  2 +
 2 files changed, 68 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/panel/raio,ra8875.yaml

new file mode 100644
index 000000000000..f6f4867495dd
@@ -0,0 +1,66 @@
+# 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: |
+  This binding is for display panels using an RAiO RA8875 controller
+  connected via SPI.
+
+allOf:
+  - $ref: panel-common.yaml#
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    const: raio,ra8875
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 25000000
+
+  display-timings:
+    $ref: /schemas/display/panel/display-timings.yaml#
+
+required:
+  - compatible
+  - reg
+  - display-timings
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        ra8875: ra8875@0 {
+            compatible = "raio,ra8875";
+            reg = <0>;
+            spi-max-frequency = <16000000>;
+
+            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

Don use "YAML binding schema". It's redundant. You add bindings.

Or better drop entire sentence, not really needed.

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 | 739 ++++++++++++++++++++++++++++++++++
 4 files changed, 759 insertions(+)
 create mode 100644 drivers/gpu/drm/tiny/ra8875.c

index 5b5a4e4b35cf..6434528c354c 100644
@@ -8449,6 +8449,12 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/display/panel/raydium,rm67191.yaml
 F:	drivers/gpu/drm/panel/panel-raydium-rm67191.c
 
+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 SAMSUNG DB7430 PANELS
 M:	Linus Walleij <[email protected]>
 S:	Maintained

index f0e72d4b6a47..0b9e3d43e931 100644
@@ -195,6 +195,19 @@ config TINYDRM_REPAPER
 
 	  If M is selected the module will be called repaper.
 
+config TINYDRM_RA8875
+	tristate "DRM support for RA8875 display panels"
+	depends on DRM && SPI
+	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-TFTM070-5V4)
+
+	  If M is selected the module will be called ra8875.
+
 config TINYDRM_SHARP_MEMORY
 	tristate "DRM support for Sharp Memory LCD panels"
 	depends on DRM && SPI

index 48d30bf6152f..17e5e7766309 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-$(CONFIG_TINYDRM_RA8875)		+= ra8875.o
 obj-$(CONFIG_TINYDRM_SHARP_MEMORY)	+= sharp-memory.o

2.55.0

All ID tables are placed together, just before 'struct xxx_driver'.

...

Please don't include <linux/mod_devicetable.h>. Both of_device_id and spi_device_id are provided by <linux/spi/spi.h> already without pulling in definitions for completely unrelated busses as dependency for your driver.

Best regards
Uwe