Hi,
Here's a follow-up on the previous discussion about the current state of DSI/DBI panel drivers, TinyDRM, and the need of a cleanup.
For the record, here is a small sum-up of the current situation:
- the current MIPI DBI code (drivers/gpu/drm/drm_mipi_dbi.c) is lagging way behind the MIPI DSI code (drivers/gpu/drm/drm_mipi_dsi.c). While the DSI code adds a proper bus support, with support for host drivers and client devices, there is no such thing with the DBI code. As such, it is currently impossible to write a standard DRM panel driver for a DBI panel.
- Even if the MIPI DBI code was updated with a proper bus, many panels and MIPI controllers support both DSI and DBI, so it would be a pain to support them without resolving to duplicating each driver.
- The panel drivers written against the DBI code are all "tinyDRM" drivers, which means that they will register a full yet simple DRM driver, and cannot be used as regular DRM panels for a different DRM driver.
- These "tinyDRM" drivers all use SPI directly, even though the panels they're driving can work on other interfaces (e.g. i8080 bus). Which means that one driver written for e.g. a ILI9341 would not work if the control interface is not SPI.
- The "tinyDRM" common code is entangled with DBI and there is no clear separation between the two. It could very well be moved to a single "tinyDRM" driver that works with a DRM panel obtained from devicetree, because the only requirement is that the panel supports a few given DCS commands.
This patchset introduces the following:
* Patch [2/6] slightly tweaks the MIPI DSI code so that it now also supports MIPI DBI over various hardware buses. Because if you think about it, DSI is just the same as DBI just on a different hardware bus. The DSI host drivers, now DSI/DBI host drivers, set compatibility bits for the hardware buses they support (DSI, DBI/i8080, DBI/SPI9, DBI/SPI+GPIO), which is matched against the hardware bus that panel drivers request.
* For the DBI panels connected over SPI, a new DSI/DBI host driver is added in patch [3/6]. It allows MIPI DBI panel drivers to be written with the DSI/DBI framework, even if they are connected over SPI, instead of registering as SPI device drivers. Since most of these panels can be connected over various buses, it permits to reuse the same driver independently of the bus used.
* Patch [4/6] adds a panel driver for NewVision NV3052C based panels. This has been successfully tested on the Anbernic RG350M handheld console, along with the dbi-spi bridge and the ingenic-drm driver.
* A TinyDRM driver for DSI/DBI panels, once again independent of the bus used; the only dependency (currently) being that the panel must understand DCS commands.
* A DRM panel driver to test the stack. This driver controls Ilitek ILI9341 based DBI panels, like the Adafruit YX240QV29-T 320x240 2.4" TFT LCD panel. This panel was converted from drivers/gpu/drm/tiny/ili9341.c.
Patches [1-4] were successfully tested on hardware. Patches [5-6] were compile-tested and runtime-tested but without hardware connected, so I'd want a Tested-by on these two.
Another thing to note, is that it does not break Device Tree ABI. The display node stays the same:
spi { ...
display@0 { compatible = "adafruit,yx240qv29", "ilitek,ili9341"; reg = <0>; spi-max-frequency = <32000000>; dc-gpios = <&gpio0 9 GPIO_ACTIVE_HIGH>; reset-gpios = <&gpio0 8 GPIO_ACTIVE_HIGH>; rotation = <270>; backlight = <&backlight>; }; };
The reason it works, is that the "adafruit,yx240qv29" device is probed on the SPI bus, so it will match with the SPI/DBI host driver. This will in turn register the very same node with the DSI bus, and the ILI9341 DRM panel driver will probe. The driver will detect that no controller is linked to the panel, and eventually register the DBI/DSI TinyDRM driver.
One drawback of this approach, is that the "adafruit,yx240qv29" must be added to the dbi-spi bridge driver (unless a custom rule is added for a "dbi-spi" fallback compatible string). I still think that it's a small price to pay to avoid breaking the Device Tree bindings.
Feedback welcome.
Cheers, -Paul
Paul Cercueil (6): dt-bindings: display: Document NewVision NV3052C DT node drm: dsi: Let host and device specify supported bus drm/bridge: Add SPI DBI host driver drm/panel: Add panel driver for NewVision NV3052C based LCDs drm/tiny: Add TinyDRM for DSI/DBI panels drm/panel: Add Ilitek ILI9341 DBI panel driver
.../display/panel/newvision,nv3052c.yaml | 69 +++ drivers/gpu/drm/bridge/Kconfig | 8 + drivers/gpu/drm/bridge/Makefile | 1 + drivers/gpu/drm/bridge/dbi-spi.c | 262 +++++++++ drivers/gpu/drm/drm_mipi_dsi.c | 9 + drivers/gpu/drm/panel/Kconfig | 18 + drivers/gpu/drm/panel/Makefile | 2 + drivers/gpu/drm/panel/panel-ilitek-ili9341.c | 345 ++++++++++++ .../gpu/drm/panel/panel-newvision-nv3052c.c | 523 ++++++++++++++++++ drivers/gpu/drm/tiny/Kconfig | 8 + drivers/gpu/drm/tiny/Makefile | 1 + drivers/gpu/drm/tiny/tiny-dsi.c | 266 +++++++++ include/drm/drm_mipi_dsi.h | 31 ++ 13 files changed, 1543 insertions(+) create mode 100644 Documentation/devicetree/bindings/display/panel/newvision,nv3052c.yaml create mode 100644 drivers/gpu/drm/bridge/dbi-spi.c create mode 100644 drivers/gpu/drm/panel/panel-ilitek-ili9341.c create mode 100644 drivers/gpu/drm/panel/panel-newvision-nv3052c.c create mode 100644 drivers/gpu/drm/tiny/tiny-dsi.c