drm/tiny: Add MIPI DBI compatible SPI driver

Add a driver that will work with most MIPI DBI compatible SPI panels.
This avoids adding a driver for every new MIPI DBI compatible controller
that is to be used by Linux. The 'compatible' Device Tree property with
a '.bin' suffix will be used to load a firmware file that contains the
controller configuration.

Example (driver will load sainsmart18.bin):

display@0 {
	compatible = "sainsmart18", "panel-mipi-dbi-spi";
...
};

v5:
- kconfig: s/DRM_KMS_CMA_HELPER/DRM_GEM_CMA_HELPER/ (Sam)
- kconfig: Add select VIDEOMODE_HELPERS (Sam)
- kconfig: Add wiki url in the description (Sam)
- Split out and use of_get_drm_panel_display_mode()(Sam)
- Only use the first compatible to look for a firmware file since the
  binding mandates 2 compatibles.
- Make having a firmware file mandatory so we can print an error
  message if it's missing to improve the user experience. It's very
  unlikely that a controller doesn't need to be initialized and if
  it doesn't, it's possible to have a firmware file containing only
  a DCS NOP.

v4:
- Move driver to drm/tiny where the other drivers of its kind are located.
  The driver module will not be shared with a future DPI driver after all.

v3:
- Move properties to DT (Maxime)
- The MIPI DPI spec has optional support for DPI where the controller is
  configured over DBI. Rework the command functions so they can be moved
  to drm_mipi_dbi and shared with a future panel-mipi-dpi-spi driver

v2:
- Drop model property and use compatible instead (Rob)
- Add wiki entry in MAINTAINERS
Acked-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220227124713.39766-6-noralf@tronnes.org

MAINTAINERS

@@ -6107,6 +6107,14 @@ T:	git git://anongit.freedesktop.org/drm/drm-misc
 F:	Documentation/devicetree/bindings/display/multi-inno,mi0283qt.txt
 F:	drivers/gpu/drm/tiny/mi0283qt.c
 
+DRM DRIVER FOR MIPI DBI compatible panels
+M:	Noralf Trønnes <noralf@tronnes.org>
+S:	Maintained
+W:	https://github.com/notro/panel-mipi-dbi/wiki
+T:	git git://anongit.freedesktop.org/drm/drm-misc
+F:	Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
+F:	drivers/gpu/drm/tiny/panel-mipi-dbi.c
+
 DRM DRIVER FOR MSM ADRENO GPU
 M:	Rob Clark <robdclark@gmail.com>
 M:	Sean Paul <sean@poorly.run>

drivers/gpu/drm/tiny/Kconfig

@@ -51,6 +51,21 @@ config DRM_GM12U320
 	 This is a KMS driver for projectors which use the GM12U320 chipset
 	 for video transfer over USB2/3, such as the Acer C120 mini projector.
 
+config DRM_PANEL_MIPI_DBI
+	tristate "DRM support for MIPI DBI compatible panels"
+	depends on DRM && SPI
+	select DRM_KMS_HELPER
+	select DRM_GEM_CMA_HELPER
+	select DRM_MIPI_DBI
+	select BACKLIGHT_CLASS_DEVICE
+	select VIDEOMODE_HELPERS
+	help
+	  Say Y here if you want to enable support for MIPI DBI compatible
+	  panels. The controller command setup can be provided using a
+	  firmware file. For more information see
+	  https://github.com/notro/panel-mipi-dbi/wiki.
+	  To compile this driver as a module, choose M here.
+
 config DRM_SIMPLEDRM
 	tristate "Simple framebuffer driver"
 	depends on DRM && MMU

drivers/gpu/drm/tiny/Makefile

@@ -4,6 +4,7 @@ obj-$(CONFIG_DRM_ARCPGU)		+= arcpgu.o
 obj-$(CONFIG_DRM_BOCHS)			+= bochs.o
 obj-$(CONFIG_DRM_CIRRUS_QEMU)		+= cirrus.o
 obj-$(CONFIG_DRM_GM12U320)		+= gm12u320.o
+obj-$(CONFIG_DRM_PANEL_MIPI_DBI)	+= panel-mipi-dbi.o
 obj-$(CONFIG_DRM_SIMPLEDRM)		+= simpledrm.o
 obj-$(CONFIG_TINYDRM_HX8357D)		+= hx8357d.o
 obj-$(CONFIG_TINYDRM_ILI9163)		+= ili9163.o