RPI 7" display touch controller

[Marek Vasut]

On 11/18/21 6:02 PM, Tim Harvey wrote:
> On Thu, Nov 18, 2021 at 4:53 AM Marek Vasut <marex at denx.de> wrote:
>>
>> On 11/18/21 2:25 AM, Tim Harvey wrote:
>>> Greetings,
>>>
>>> I'm trying to get a RPI 7" touchscreen display working on an IMX8MM
>>> board and while I've been able to get the MIPI DSI display and
>>> backlight working I still can't seem to figure out the touch
>>> controller.
>>>
>>> It's supposed to have an FT5406 controller on it without an interrupt
>>> so I added polling support drivers/input/touchscreen/edt-ft5x06.c
>>> which I was able to verify using another touchscreen with that
>>> controller but when reading data from the FT5406 on the RPI controller
>>> the data does not make sense.
>>>
>>> These panels appear to route the I2C from the FT5406 to a STM32F103
>>> MPU that then provides a different I2C slave interface to the 15pin
>>> connector that I'm connected to. On that I2C interface I see an i2c
>>> slave at 0x45 which is managed by the regulator driver Marek wrote
>>> (drivers/regulator/rpi-panel-attiny-regulator.c) and there is also an
>>> i2c slave at 0x38 which I assumed was the FT5406 but I believe the MPU
>>> is perhaps obfuscating that touch data.
>>>
>>> Anyone have any ideas on how to make that touch controller useful?
>>
>> Look around:
>> https://github.com/dh-electronics/meta-dhsom-stm32-bsp/blob/dunfell-3.1/recipes-kernel/linux/linux-stable/5.10/dh-stm32mp1-dhsom/0038-ARM-dts-stm32-Add-AV96-DTO-for-DH-644-100-DSI-mezzan.patch
> 
> Marek,
> 
> Thanks. This dt overlay actually disables the touchscreen controller
> with a note that the IRQ must be hooked up to work. Did you actually
> wire up an IRQ and get it to work? I implemented polling mode for the
> controller but the data did not make sense.

The touchscreen IRQ line is accessible on some pin header on the 7" 
display control board I think, so you can attach it manually to your 
development board that way. I have a new version of that AV96 adapter 
board here now, I just didn't get to assembling it yet ... so, feel free 
to add that one IRQ patchwire and try it.

> This dt overlay also interests me as I am also wanting to get some
> overlays in the kernel tree [1]. I'm curious if you have any thoughts
> on why there are currently no overlays in the mainline tree.
> 
> 1 - https://lore.kernel.org/linux-arm-kernel/20211115202426.16114-1-tharvey@gateworks.com/T/

It would be nice to upstream the DTOs, I think the reason why they're 
not upstream is because the DTO support is still incomplete, but I might 
be wrong. Thanks for pointing this patch out, I'll keep an eye on it.