Re: [PATCH 1/3] treewide: Remove OF_PRIOR_STAGE from RISC-V boards

[Zong Li <zong.li@sifive.com>]

On Wed, Sep 29, 2021 at 6:17 PM Ilias Apalodimas
<ilias.apalodimas@linaro.org> wrote:
>
> On Wed, Sep 29, 2021 at 12:02:16PM +0300, Ilias Apalodimas wrote:
> > Hi Zong,
> >
> > [...]
> >
> > > > diff --git a/board/sifive/unleashed/unleashed.c b/board/sifive/unleashed/unleashed.c
> > > > index 8cd514df3005..7e89c3f740a7 100644
> > > > --- a/board/sifive/unleashed/unleashed.c
> > > > +++ b/board/sifive/unleashed/unleashed.c
> > > > @@ -116,12 +116,10 @@ int misc_init_r(void)
> > > >
> > > >  void *board_fdt_blob_setup(void)
> > > >  {
> > > > -       if (IS_ENABLED(CONFIG_OF_SEPARATE)) {
> > > > -               if (gd->arch.firmware_fdt_addr)
> > > > -                       return (ulong *)gd->arch.firmware_fdt_addr;
> > > > -               else
> > > > -                       return (ulong *)&_end;
> > > > -       }
> > > > +       if (gd->arch.firmware_fdt_addr)
> > > > +               return (void *)gd->arch.firmware_fdt_addr;
> > > > +       else
> > > > +               return (void *)&_end;
> > > >  }
> > >
> > > I was wondering if we need to check CONFIG_OF_BOARD here? I'm not sure
> > > whether we should distinguish the value of a1 register which is
> > > meaningless. It means that if we don't expect the device tree to be
> > > passed by prior stage, then the a1 register might be a trash value at
> > > the beginning, so it would still return the arch.firmware_fdt_addr
> > > here, rather than _end.
> >
> > I thought about it as well.  Those boards were configured up to now with
> > 'CONFIG_OF_SEPARATE'.  Which means we are looking at an existing issue?
> > IOW the device tree was passed as part of U-Boot,  which would mean a1 would
> > have had thrash as well.  Maybe a1 always has a valid DT on those boards
> > so we never noticed?
> >
> >
> > > And do you think that we should enable the
> > > CONFIG_OF_BOARD for unmatched and unleashed? Because it seems to me
> > > that we actually pass the device tree by prior stage (i.e. OpenSBI).
> >
> > Yes in that case what you request makes sense for unmatched/unleashed.
> > Return gd->arch.firmware_fdt_addr in OF_BOARD is selected otherwise return
> > _end (instead of the current check).
> > If that sounds good to you I'll send a v2
>
> Looking a bit more at it...
> Apparently those boards boot from SPL.  So it's SPL->OpenSBI->U-Boot.
> By having the config as OF_SEPARATE the *U-Boot* DTB is used. SPL passes it to
> OpenSBI and OpenSBI passes it on a1 to U-Boot proper.  That's why the register
> reading works for that config.
>
> In that case the pre-existing code is 'wrong' as well,  since the DTB is
> not at _end,  but the bogus path is never taken...
> (check the __weak board_fdt_blob_setup for details).
>

If I remember correctly, the SPL would calculate the size of u-boot
proper, and then put the DTB at the end of  u-boot proper, so the DTB
would fortuitously be put at the _end location.

> So I think I'll send a v2, keeping the config as-is and fixing the return
> address of the DTB in case OF_BOARD is ever selected.
>

Yes, it seems to me that we could use a config to separate the case
between the prior stage and the _end. Just note that, there is a patch
on the fly, it modifies the same snippet of code, you might need to
update your code based on top of it.
https://lists.denx.de/pipermail/u-boot/2021-September/460378.html

> Cheers
> /Ilias
> >
> > [...]
> >
> > Regards
> > /Ilias