Re: [PATCH 0/6] drm/tiny/st7735r: Match up with staging/fbtft driver

[David Lechner <david@lechnology.com>]

On 12/1/21 8:52 AM, Maxime Ripard wrote:
> Hi Noralf,
> 
> On Tue, Nov 30, 2021 at 03:30:11PM +0100, Noralf Trønnes wrote:
>> Den 29.11.2021 10.39, skrev Maxime Ripard:
>>> On Wed, Nov 24, 2021 at 04:03:07PM -0600, David Lechner wrote:
>>>> On 11/24/21 9:07 AM, Noralf Trønnes wrote:
>>> I agree that it doesn't really fit in the DT either though. Noralf, what
>>> kind of data do we need to setup a display in fbtft? The init sequence,
>>> and maybe some enable/reset GPIO, plus some timing duration maybe?
>>>
>>> There's one similar situation I can think of: wifi chips. Those also
>>> need a few infos from the DT (like what bus it's connected to, enable
>>> GPIO, etc) and a different sequence (firmware), sometimes different from
>>> one board to the other.
>>>
>>> Could we have a binding that would be something like:
>>>
>>> panel@42 {
>>> 	 compatible = "panel-spi";
>>> 	 model = "panel-from-random-place-42";
>>> 	 enable-gpios = <&...>;
>>> }
>>>
>>> And then, the driver would request the init sequence through the
>>> firmware mechanism using a name generated from the model property.
>>>
>>> It allows to support multiple devices in a given system, since the
>>> firmware name wouldn't conflict, it makes a decent binding, and users
>>> can adjust the init sequence easily (maybe with a bit of tooling)
>>>
>>> Would that work?
>>
>> I really like this idea. An added benefit is that one driver can handle
>> all MIPI DBI compatible controllers avoiding the need to do a patchset
>> like this for all the various MIPI DBI controllers. The firmware will
>> just contain numeric commands with parameters, so no need for different
>> controller drivers to handle the controller specific command names.
>>
>> The following is a list of the MIPI DBI compatible controllers currently
>> in staging/fbtft: ili9341, hx8357d, st7735r, ili9163, ili9163, ili9163,
>> ili9163, ili9486, ili9481, tinylcd, s6d02a1, s6d02a1, hx8340bn, ili9340.
>>
>> The compatible needs to be a bit more specific though since there are 2
>> major SPI protocols for these display: MIPI DBI and the one used by
>> ILI9325 and others.
>>
>> The full binding would be something like this:
>>
>> panel@42 {
>> 	compatible = "panel-mipi-dbi-spi";
>> 	model = "panel-from-random-place-42";
>>
>> 	/* The MIPI DBI spec lists these powers supply pins */
>> 	vdd-supply = <&...>;
>> 	vddi-supply = <&...>;
>>
>> 	/* Optional gpio to drive the RESX line */
>> 	reset-gpios = <&...>;
>>
>> 	/*
>> 	 * D/CX: Data/Command, Command is active low
>> 	 * Abcense: Interface option 1 (D/C embedded in 9-bit word)
>> 	 * Precense: Interface option 3
>> 	 */
>> 	dc-gpios = <&...>;
>>
>> 	/*
>> 	 * If set the driver won't try to read from the controller to see
>> 	 * if it's already configured by the bootloader or previously by
>> 	 * the driver. A readable controller avoids flicker and/or delay
>> 	 * enabling the pipeline.
>> 	 *
>> 	 * This property might not be necessary if we are guaranteed to
>> 	 * always read back all 1's or 0's when MISO is not connected.
>> 	 * I don't know if all setups can guarantee that.
>> 	 */
>> 	write-only;
>>
>> 	/* Optional ref to backlight node */
>> 	backlight = <&...>;
>> }
> 
> It looks decent to me. We'll want Rob to give his opinion though, but it
> looks in a much better shape compared to what we usually have :)
> 
>> Many of these controllers also have a RGB interface option for the
>> pixels and only do configuration over SPI.
>> Maybe the compatible should reflect these 2 options somehow?
> 
> I think we'll want a "real" panel for RGB, with its own compatible
> though. We have a few of these drivers in tree already, so it's better
> to remain consistent.
> 
> Maxime
> 

I'm on board with the idea of the init sequence as firmware as well.

It looks like Rob might have missed this thread, so maybe just apply
the acked patches and submit a v2 with the firmware implementation?