[U-Boot] [PATCH 21/51] common: Extend board-specific DT fixup

[Simon Glass]

Hi Mario,

On 14 July 2017 at 05:55, Mario Six <mario.six at gdsys.cc> wrote:
> Commit 2a79275 ("dm: Add callback to modify the device tree")
> implemented a board-specific callback that can modify U-Boot's device
> tree before relocation to accomodate a range of hardware variations of
> certain boards.
>
> However, this approach only turns out to be useful when the copy of the
> device tree before relocation is actually writeable. If e.g. a device
> boots out of a NOR flash, this scheme does not work, since the
> modification of the flash's contents is not possible, and the unmodified
> device tree is relocated and used by U-Boot.
>
> To circumvent this problem, we split the modification process into two
> phases.
>
> In phase one we only collect information about the board by querying the
> hardware (reading GPIO values, probing I2C chips, etc.), and store the
> obtained information in a special, board-specific structure that is part
> of the global data structure. This phase runs prior to relocation, and
> utilizes the pre-relocation DM to query hardware information.
>
> In phase two, we read the information back from the structure, and do
> the actual manipulation of the device tree. This phase occurs *after*
> the relocation of the U-Boot image, but before the driver model is
> initialized from the device tree. Since the device tree lives in RAM
> alongside the U-Boot image after relocation, the tree is definitely
> writeable at this point.
>
> Each phase is implemented by a board-specific callback function: phase
> one by board_fix_fdt_get_info, which takes no arguments, and phase two
> by board_fix_fdt_change, which takes the writeable device tree blob as
> its sole argument. Since the structure where the gathered hardware
> information is stored is necessarily board-dependent, we create a
> include file where the boards utilizing the functionality can define
> their individually needed structures.
>
> This commit also adapts the controlcenterdc board's fixup function to
> the new schem

Thanks for the clear explanation.

I have two ideas:

- Can we move the call to the existing function to after reloc_fdt(),
when the DT is in RAM?

- Or can we move this board to use a livetree and adjust the DT using
livetree functions instead? That might be more efficient.

Regards,
Simon