[U-Boot] sunxi: add custom board

[Giulio Benetti]

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?

We only need a road to follow to be upstreamed later.

Thanks a lot
Best regards
-- 
Giulio Benetti
CTO

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