On Fri, Jun 4, 2021 at 5:51 PM Palmer Dabbelt [off-list ref] wrote:

On Fri, 04 Jun 2021 06:08:05 PDT (-0700), Arnd Bergmann wrote:

quoted

On Fri, Jun 4, 2021 at 2:06 PM Alexandre Ghiti [off-list ref] wrote:

quoted

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@ghiti.fr>

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

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