Re: [PATCH] fdt_support: add optional board_rng_seed() hook

[Simon Glass <sjg@chromium.org>]

Hi Rasmus,

On Tue, 23 Aug 2022 at 07:06, Rasmus Villemoes
<rasmus.villemoes@prevas.dk> wrote:
>
> On 23/08/2022 15.38, Simon Glass wrote:
>
> >> +/**
> >> + * board_rng_seed() - Provide a seed to be passed via /chosen/rng-seed
> >> + *
> >> + * This function is called if CONFIG_BOARD_RNG_SEED is set, and must
> >> + * be provided by the board. It should return, via @buf, some suitable
> >> + * seed value to pass to the kernel.
> >> + *
> >> + * @param buf         A struct abuf for returning the seed and its size.
> >> + * @return            0 if ok, negative on error.
> >> + */
> >> +int board_rng_seed(struct abuf *buf);
> >
> > Instead of yet another hook, can we use EVT_FT_FIXUP? An even better
> > option might be to use EVT_FT_FIXUP and then call a UCLASS_BOARD
> > method to obtain the information.
>
> I didn't know there was anything called EVT_FT_FIXUP, and from grepping,
> it seems suffer the same problem as ft_board_setup() as I mention,
> namely running after the command line (aka /chosen/bootargs) has been
> set up.

If that is the only problem, then you could add another event for
doing an earlier fixup.

>
> Also, I can't see how it can actually affect the blob being passed to
> the kernel, doesn't
>
>                 fixup.tree = oftree_default();
>                 ret = event_notify(EVT_FT_FIXUP, &fixup, sizeof(fixup));
>
> mean that fixup.tree points at U-Boot's control fdt rather than the blob
> that will be passed as the kernel's fdt? That seems wrong.

Yes that is wrong for many platforms. We should probably just change
it, but there is a complication.

My recent series made a start at supporting writing to a DT using the
ofnode interface. See vbe_simple_test_base() for some comments on the
current state. You could require OF_LIVE to be enabled for your new
feature.

Ideally I'd like to see ofnode used for all devicetree access, but it
will need to be done in stages. In the meantime we should try to head
in that direction.

Regards,
Simon