Hi Noralf,
Le dim. 14 juin 2020 à 18:36, Noralf Trønnes noralf@tronnes.org a écrit :
Den 07.06.2020 15.38, skrev Paul Cercueil:
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.
This patchset introduces the following:
- It slightly tweaks the MIPI DSI code so that it supports MIPI DBI
over various buses. This patch has been tested with a non-upstream DRM panel driver for a ILI9331 DBI/8080 panel, written with the DSI framework (and doesn't include <drm/drm_mipi_dbi.h>), and non-upstream DSI/DBI host driver for the Ingenic SoCs.
- A SPI DBI host driver, using the current MIPI DSI framework. It
allows MIPI DSI/DBI drivers to be written with the DSI 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.
- 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.
I would like to emphasize that while it has been compile-tested, I did not test it with real hardware since I do not have any DBI panel connected over SPI. I did runtime-test the code, just without any panel connected.
Another thing to note, is that it does not break Device Tree ABI. The display node stays the same:
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.
I can't stress it enough that this is a RFC, so it still has very rough edges.
I don't know bridge and dsi drivers so I can't comment on that, but one thing I didn't like is that the DT compatible string has to be added to 2 different modules.
That's a minimal drawback for a perfectly architectured design ;)
As an example, a MI0283QT panel (ILI9341) supports these interface options:
SPI Panel setup/control and framebuffer upload over SPI
SPI + DPI Panel setup/control over SPI, framebuffer scanout over DPI
Parallel bus Panel setup/control and framebuffer upload over parallel bus
My suggestion is to have one panel driver module that can support all of these like this:
For 1. and 2. a SPI driver is registered and if I understand your example correctly of_graph_get_port_by_id() can be used during probe to distinguish between the 2 options and register a full DRM driver for
and add a DRM panel for 2.
For 3. a DSI driver is registered (adapted for DBI use like you're suggesting).
That means basically having two entry points per DBI driver, one as DSI device and one as SPI device, the latter doing the job of the current DBI-SPI bridge. I think i would be cleaner to just have duplicated strings with the DBI-SPI bridge.
Cheers, -Paul
Note that the interface part of the controller initialization will differ between these, the panel side init will be the same I assume.
Noralf.