[U-Boot] sunxi: add custom board

[Giulio Benetti]

Il 26/10/2018 13:06, Maxime Ripard ha scritto:
> On Thu, Oct 25, 2018 at 12:57:54PM +0200, Giulio Benetti wrote:
>> Hello Maxime,
>>
>> Il 24/10/2018 19:59, Maxime Ripard ha scritto:
>>> On Wed, Oct 24, 2018 at 03:59:56PM +0200, Giulio Benetti wrote:
>>>> Hello Jagan and Maxime,
>>>>
>>>> I've looked around a lot, but I can't find a way to use the board/sunxi:
>>>> http://git.denx.de/?p=u-boot.git;a=tree;f=board/sunxi;h=304ee6b4cc8e075759d3bd0beb250b56f6901702;hb=HEAD
>>>>
>>>> to fit what we need.
>>>>
>>>> We have 5 gpios that control the max current setting on
>>>> current-driver for Backlight biasing shunt kathode resistor, and I
>>>> don't know where to place the code to set those pins.
>>>>
>>>> I would like to avoid to create another new board if possible, since
>>>> board/sunxi has everything we need to make our board operative.
>>>> In general, is there some sort of __weak__ hooks to be used to extend an
>>>> existing board?
>>>> Because I understand that probably you wouldn't add this code I'm talking
>>>> about inside board/sunxi.
>>>>
>>>> This request is done with idea to upstream patch for this board.
>>>>
>>>> Can you help me?
>>>
>>> If that's backlight related, maybe you can just create a new backlight
>>> driver?
>>
>> If it makes sense for sure we can.
>>
>> But please can you take a look at the schematics of current-driver with
>> mosfets biasing power?
>> https://pasteboard.co/HK4ChzF.png
>> As you can see we bias BKL_K (Backlight Kathode) to slightly influence the
>> shunt(R81+R76).
>> I don't know how it could be useful for the others.
>>
>> We use that to handle different displays with the same board(A20 based).
>>
>> So does it make sense to write a driver?
>> And if yes, I would think about adding:
>> backlight_current.c under u-boot/drivers/video
>> or another option could be to write a driver under:
>> u-boot/drivers/power
>>
>> What do you think?
> 
> Maybe you can just create a regulator driver, with each current step
> describing a step, just like gpio-regulator is doing for the voltage.

That's a perfect example, thanks for pointing me.

I would call it gpio-current-regulator and then I would place multiple 
"states" instead of the current 2 states of gpio-regulator.

Does it sound good?

After some work maybe we should submit an RFC, right?

Thank you
Best regards
-- 
Giulio Benetti
CTO

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