Re: [PATCH -fixes] riscv: Fix BUILTIN_DTB for sifive and microchip soc

[Arnd Bergmann]

On Fri, Jun 4, 2021 at 5:51 PM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
> On Fri, 04 Jun 2021 06:08:05 PDT (-0700), Arnd Bergmann wrote:
> > On Fri, Jun 4, 2021 at 2:06 PM Alexandre Ghiti <alex@xxxxxxxx> wrote:
> >>
> >> Fix BUILTIN_DTB config which resulted in a dtb that was actually not built
> >> into the Linux image: in the same manner as Canaan soc does, create an object
> >> file from the dtb file that will get linked into the Linux image.
> >>
> >> Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> >
> > Along the same lines as the comment that Jisheng Zhang made on the fixed
> > address, building a dtb into the kernel itself fundamentally breaks generic
> > kernel images.
> >
> > I can understand using it on K210, which is extremely limited and wouldn't
> > run a generic kernel anyway, but for normal platforms like microchip and
> > sifive, it would be better to disallow CONFIG_BUILTIN_DTB in Kconfig
> > and require a non-broken boot loader.
>
> When we first added BUILTIN_DTB we actually had a compatibility
> mechanism in there.  There isn't enough in the ISA to handle board
> compatibility, but we were hoping to get something to deal with that.
> It didn't pan out so we dropped the compatibility mechanism, which is
> how we ended up here.
>
> Maybe the right thing to do here is to add some sort of "be compatible
> with the platform spec" Kconfig, which we could then use to disallow all
> these features that result in non-portable kernels?

Yes, I should have read your email before I replied with the same
suggestion to Vitaly ;-)

       Arnd