[PATCH 2/3] of/fdt: introduce of_scan_flat_dt_subnodes and of_get_flat_dt_phandle

[Rob Herring]

On Wed, Apr 5, 2017 at 7:38 PM, Nicholas Piggin <npiggin at gmail.com> wrote:
> On Thu, 06 Apr 2017 06:58:01 +1000
> Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:
>
>> On Wed, 2017-04-05 at 10:58 -0500, Rob Herring wrote:
>> > Well, I'd like to avoid expanding usage of flat DT parsing in the
>> > kernel. But you could just put this function into arch/powerpc and I'd
>> > never see it, but I like that even less. Mainly, I just wanted to
>> > raise the point.
>> >
>> > Your argument works until you need that setup in assembly code, then
>> > you are in the situation that you need to either handle the setup in
>> > bootloader/firmware or have an simple way to determine that condition.
>>
>> The main issue is that changing that is a very very invasive change in
>> an extremely fragile and rather nasty area of code shared by 32 and 64-
>> bit for which we don't even have easy access to all the machines to
>> test with anymore :)
>>
>> It's probably not impossible, but it would delay the new cpu feature
>> stuff that Nick is making by a lot, probably monthes, making it nearly
>> impossible to get back into distros etc...
>>
>> So while it might be something to consider, I would definitely keep
>> that as a separate unit of work to do later.
>
> Yeah, it's no longer a "drop in" replacement for existing features
> testing if we do this, which makes it hard to backport too (we will
> need this for compatibility with future firmware, so it will have to
> go into distro kernels.)
>
> Given that it's quite a small addition to of/fdt code, hopefully
> that gives you a reasonable justification to accept it.
>
> If you prefer not to, that's okay, but I think we would have to carry
> it in arch/powerpc at least for a time, because of the schedule we're
> working to for POWER9 enablement. As a longer term item I agree with you
> and Ben, it would be worth considering unflattening earlier.

As I mentioned, keeping it in arch/powerpc I like even less. So this is fine.

Rob