[U-Boot] sunxi: add custom board

[Maxime Ripard]

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.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com