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

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

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).

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.

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