[RFC PATCH 2/2] board: ti: am65x: Move to using Extension framework

[Roger Quadros]

On 06/10/2023 16:26, Köry Maincent wrote:
> On Wed, 4 Oct 2023 15:39:23 +0300
> Roger Quadros <rogerq at kernel.org> wrote:
> 
> Hello,
> Thanks for adding me in cc. Also it seems I forgot to add myself to MAINTAINERS
> for the extension_board.c file.
> 
>>>>> Before this goes too far I think this should move to using a linker
>>>>> list to declare the driver (or a driver-model driver if you prefer,
>>>>> but that might be overkill).  
>>
>> So I've been working on this on the side and got linker list way working
>> with custom script booting but as soon as I move to standard boot flow
>> it no longer works. This is because there is no code in place to
>> apply the overlay and pass it to next stage e.g. EFI.
>>
>> I see the following note at
>> https://elixir.bootlin.com/u-boot/latest/source/boot/bootmeth_efi.c#L304
>>
>> "
>>                 /*
>>                  * TODO: Apply extension overlay
>>                  *
>>                  * Here we need to load and apply the extension overlay. This
>> is
>>                  * not implemented. See do_extension_apply(). The extension
>>                  * stuff needs an implementation in boot/extension.c so it is
>>                  * separate from the command code. Really the extension stuff
>>                  * should use the device tree and a uclass / driver interface
>>                  * rather than implementing its own list
>>                  */
>> "
> 
> I agreed that the extension implementation should move in boot/extension.c or
> common for general use. I am wondering what the advantage of creating an uclass
> interface?
> I am not an uclass expert but there is no per driver ops and usage. What do you
> dislike about using its own list?

There would be per platform ops for probing the extension cards in a platform
specific way.

I already have a linker list way of doing this but stumbled upon Simon's
comments about using uclass for this.

> 
>> Another note at
>> https://elixir.bootlin.com/u-boot/latest/source/cmd/extension_board.c#L198
>>
>> "/* extensions should have a uclass - for now we use UCLASS_SIMPLE_BUS uclass
>> */"
>>
>> So are we better off implementing a class driver for extension stuff?
> 
> I think the first point should be to move it in common or boot and makes it
> generic for using the extension function everywhere. I will let Simon answer
> about the uclass part.
> 
> Regards,

-- 
cheers,
-roger