Re: [PATCH] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param

[Marek Szyprowski]

On 10.12.2025 15:07, Rob Herring wrote:
> On Tue, Dec 9, 2025 at 6:20 PM Oreoluwa Babatunde
> <oreoluwa.babatunde@xxxxxxxxxxxxxxxx> wrote:
>> When initializing the default cma region, the "cma=" kernel parameter
>> takes priority over a DT defined linux,cma-default region. Hence, give
>> the reserved_mem framework the ability to detect this so that the DT
>> defined cma region can skip initialization accordingly.
> Please explain here why this is a new problem. Presumably the
> RESERVEDMEM_OF_DECLARE hook after commit xxxx gets called before the
> early_param hook. And why is it now earlier?
>
> I don't really like the state/ordering having to be worried about in 2 places.

I also don't like this spaghetti, but it originates from 
commit 8a6e02d0c00e ("of: reserved_mem: Restructure how the reserved 
memory regions are processed") and the first fixup for it: 2c223f7239f3 
("of: reserved_mem: Restructure call site for 
dma_contiguous_early_fixup()").

It looks that it is really hard to make reserved memory 
initialization fully dynamic assuming that the cma related fixups have 
to be known before populating kernel memory pages tables. I also advised 
in 
https://lore.kernel.org/all/be70bdc4-bddd-4afe-8574-7e0889fd381c@xxxxxxxxxxx/ 
to simply increase the size of the static table to make it large enough for the sane use cases, but 
it turned out that this approach was already discussed and rejected:
https://lore.kernel.org/all/1650488954-26662-1-git-send-email-quic_pdaly@xxxxxxxxxxx/

Maybe it would make sense to revert the mentioned changes and get back 
to such simple approach - to make the size of the static table 
configurable in the Kconfig?

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland