On Tue, Jul 07, 2020 at 04:32:25PM +0200, Noralf Trønnes wrote:
(cc Dillon)
Den 03.07.2020 19.26, skrev Sam Ravnborg:
Hi Noralf/Paul.
Trying to stir up this discussion again.
On Sun, Jun 14, 2020 at 06:36:22PM +0200, Noralf Trønnes wrote:
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.
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
To continue the configurations we should support:
- Panels where the chip can be configured to SPI, SPI+DPI, Parallel bus (as detailed by Noralf above)
- Panels that supports only 6800 or 8080 - connected via GPIO pins or memory mapped (maybe behind some special IP to support this) Command set is often special.
We will see a number of chips with many different types of displays. So the drivers should be chip specific with configuration depending on the connected display.
What I hope we can find a solution for is a single file/driver that can support all the relevant interface types for a chip. So we would end up with a single file that included the necessary support for ili9341 in all interface configurations with the necessary support for the relevant displays.
I do not know how far we are from this as I have not dived into the details of any of the proposals.
In an ideal world I would have liked to see the MIPI DBI parallel interface implemented using a new Linux parallel bus type. It could have drivers for gpio bitbanging and mmio in addition to other hw specific drivers. Now we could have a drm_mipi_dbi DRM driver that registers as a SPI client driver and a Parallel bus client driver. Or it can be a component driver for the existing DRM driver on the SoC.
I had plans to do this and made a prototype, but dropped it since it would probably require a lot of work getting in a new Linux bus type.
Channelling my inner Greg KH:
Please just create a new bus, it should be quite easy and boilerplate is manageable.
Greg, did I get this right? Maybe any recommendations for a simple parallel bus with perhaps different register access paths depending upon how it's all wired up exactly? -Daniel
However if we're going to treat this parallel bus only as a MIPI DBI display interface but support gpio bitbanging and mmio as well, then we could add DRM drivers for each MIPI DBI bus (that don't have special parallel bus hw):
- mipi-dbi-spi
- mipi-dbi-gpio
- mipi-dbi-mmio
These drivers will register as a mipi_dsi_host adapted like Paul suggested.
The panel drivers will be mipi_dsi_drivers. Now the panels should work regardless of bus type. They probably need to know about the bus type, at least whether the parallell bus is 8-bit or 16-bit wide.
The current MIPI DBI SPI drivers (drm/tiny) will need to be treated specially to keep working with old Device Trees when moved over to drm/panel.
Noralf.
My suggestion is to have one panel driver module that can support all of these like this:
So I think we agree here.
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 1. and add a DRM panel for 2.
For 3. a DSI driver is registered (adapted for DBI use like you're suggesting).
Note that the interface part of the controller initialization will differ between these, the panel side init will be the same I assume.
Sam