[PATCH 2/3] drm/panel: Add DT bindings for Ilitek ILI9322

[Linus Walleij]

On Sun, Sep 24, 2017 at 10:36 PM, Rob Herring <robh at kernel.org> wrote:
> On Wed, Sep 20, 2017 at 6:56 AM, Linus Walleij <linus.walleij at linaro.org> wrote:
>> On Sat, Sep 2, 2017 at 11:17 PM, Linus Walleij <linus.walleij at linaro.org> wrote:

>>>> Normally, we the physical panel is described which would imply all these
>>>> settings. Are there lots of panels with this controller that would
>>>> justify all these settings?
>>>
>>> The datasheet for the ili9322 just says it "drives panels" essentially.
>>> Googling around gives at hand that it is used pretty frequently in
>>> Shenzhen China for adapting different off-the-shelf panels to
>>> different inputs.
>>>
>>> I can't really answer how many of these products that run one or
>>> another OS using device tree to describe the configuration. It feels more
>>> like I'm paving the road for others to travel.
>
> Not really a road I want to pave and encourage others.

It's good when maintainers say "no"! :)

>>>>> +  - ilitek,entry-mode: the panel can be connected to various input streams
>>>>> +    and four of them can be selected by electronic straps on the display.
>>>>> +    However it is possible to select another mode or override the
>>>>> +    electronic default with this property. Valid values:
>>>>> +    0: 8 bit serial RGB through
>>>>> +    1: 8 bit serial RGB aligned
>>>>> +    2: 8 bit serial RGB dummy 320x240
>>>>> +    3: 8 bit serial RGB dummy 360x240
>>>>> +    4: disabled
>>>>> +    5: 24 bit parallel RGB through
>>>>> +    6: 24 bit parallel RGB aligned
>>>>> +    7: 24 bit YUV 640Y 320CbCr
>>>>> +    8: 24 bit YUV 720Y 360CbCr
>>>>> +    9: disabled
>>>>> +    10: 8 bit ITU-R BT.656 720Y 360CbCr
>>>>> +    11: 8 bit ITU-R BT.656 640Y 320CbCr
>>>>
>>>> To some extent, we have some standard bindings to describe this.
>>>
>>> I don't find any. Maybe I'm looking in the wrong places :(
>
> I guess bus-width is all we have. Normally, this is all implied by the
> compatible strings of either the controller, panel or both.
>
> Another way to look at it is, we already have support for lots of
> panels and controllers. If those haven't needed to specify this
> information, then why do you?

It's a question about devicetree vs driver configuration data altogether.
An intuitive thing, gray area. Your intuition is likely better.

I feel the same about the people who push too much pin control
data into the device tree instead of the driver so I understand the
issue. (If it is that.)

>>> Also the input modes of ili9322 is coupled with resolution so
>>> it would need two more cells or so for resolution so I feel
>>> it would over-complicate things for these 12 enumerators.
>>
>> Can we proceed with these patches?
>>
>> Any opinion from DT or panel maintainers?
>
> You have my opinion. I don't think Thierry's will be different.
>
> My suggestion is to move the settings you need into the panel driver
> and out of DT. We can always move things to DT later if it makes
> sense.

Sure thing. I will take the approach of compatible string like this:

compatible = "ilitek,ili9322", "dlink,dir685-panel";

And use the latter compatible to set up all the stuff in the panel
driver, what about that?

Yours,
Linus Walleij