linux-kernel - Re: [PATCH v2] powerpc: drop page_is_ram() and walk_system_ram

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Date:   Tue, 05 Feb 2019 21:04:03 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] powerpc: drop page_is_ram() and walk_system_ram_range()

Christophe Leroy <christophe.leroy@....fr> writes:
> Le 04/02/2019 à 11:24, Michael Ellerman a écrit :
>> Christophe Leroy <christophe.leroy@....fr> writes:
>> 
>>> Since commit c40dd2f76644 ("powerpc: Add System RAM to /proc/iomem")
>>> it is possible to use the generic walk_system_ram_range() and
>>> the generic page_is_ram().
>>>
>>> To enable the use of walk_system_ram_range() by the IBM EHEA
>>> ethernet driver, the generic function has to be exported.
>> 
>> I'm not sure if we have a policy on that, but I suspect we'd rather not
>> add a new export on all arches unless we need to. Especially seeing as
>> the only user is the EHEA code which is heavily in maintenance mode.
>
> If you take the exemple of function walk_iomem_res_desc(), that's 
> similar. It is only used by x86 it seems and exported for nvdimm/e820 
> driver only.
>
> See commit d76401ade0bb6ab0a7 ("libnvdimm, e820: Register all pmem 
> resources")

OK. Which begs the question whether we need both exported. It looks like
you could probably use walk_iomem_res_desc() with the right flags to do
the same thing as walk_system_ram_range().

>> I'll put the export in powerpc code and make sure that builds.
>
> I thought there was a rule that EXPORT_SYMBOL has to immediately follow 
> the function it exports. At least checkpatch checks for that.

Yeah that is a rule. But rules are made to be broken :)

I'll merge it for now with the export in powerpc code, if we want to we
can do a separate patch to move that export into generic code and get
acks for that.

cheers