Re: [PATCH 2/4] dt-bindings: Document the Raspberry Pi Touchscreen nodes.

Eric Anholt
2017-05-22T20:51:45Z

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Laurent Pinchart <laurent.pinchart@ideasonboard.com> writes:

> Hi Archit,
>
> On Friday 19 May 2017 14:24:36 Archit Taneja wrote:
>> On 05/18/2017 08:25 PM, Laurent Pinchart wrote:
>> > On Thursday 18 May 2017 13:56:19 Archit Taneja wrote:
>> >> On 05/17/2017 12:16 AM, Eric Anholt wrote:
>> >
>> > [snip]
>> >
>> >>> In terms of physical connections:
>> >>> [15-pin "DSI" connector on 2835]
>> >>> | I2C | DSI
>> >>> / \ SPI |
>> >>> [TS] [Atmel]------[TC358762]
>> >>> \ |
>> >>> \PWM |
>> >>> \ | DPI
>> >>>
>> >>> [some backlight]------[some unknown panel]
>> >>>
>> >>> The binding I'm trying to create is to expose what's necessary for a
>> >>> driver that talks I2C to the Atmel, which then controls the PWM and does
>> >>> the command sequence over SPI to the Toshiba that sets up its end of the
>> >>> DSI link.
>> >>
>> >> The bridge (Atmel + TC358762 combination) here looks like it's primarily
>> >> an i2c device (i.e, the control bus is i2c). Therefore, the drm-bridge
>> >> driver here should be an i2c driver instead of a mipi_dsi_driver.
>> >
>> > Glad to see we agree, that's what I've proposed in a separate answer :-)
>> > I'd go one step further though, there should be no DRM bridge, just a DRM
>> > panel.
>>
>> If the PCB containing the controller chips and the panel are part of a
>> single casing, and the set up won't work with another panel, then yeah, I
>> agree. If the bridge chips are on a separate adapter board, and there is a
>> possibility to connect other panels, then maybe a separate DRM bridge and a
>> DRM panel might be a safer bet.
>
> I thought it was a single black box, but upon closer inspection there's a
> separate PCB with the Microcontroller and TC358762.
>
> Eric, do you know if it's possible to exchange the panel for another one (and
> not just an model with identical features from another vendor, but another
> panel with a different mode for instance) without reprogramming the
> microcontroller, or is the bridge board tied to the panel model ?

Not without finding some other panel with equivalent non-standard
connectors / doing your own soldering, at a minimum. And we don't know
what kind of programming the microcontroller does, since it's a black
box.

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