linux-kernel - Re: [RFC 2/4] arch-topology: add a default implementation of store_cpu

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Date:   Fri, 8 Jul 2022 11:57:05 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <sudeep.holla@....com>, <gregkh@...uxfoundation.org>
CC:     <geert@...ux-m68k.org>, <Conor.Dooley@...rochip.com>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <palmer@...osinc.com>, <aou@...s.berkeley.edu>,
        <catalin.marinas@....com>, <will@...nel.org>, <rafael@...nel.org>,
        <Daire.McNamara@...rochip.com>, <niklas.cassel@....com>,
        <damien.lemoal@...nsource.wdc.com>, <zong.li@...ive.com>,
        <kernel@...il.dk>, <hahnjo@...njo.de>, <guoren@...nel.org>,
        <anup@...infault.org>, <atishp@...shpatra.org>,
        <changbin.du@...el.com>, <heiko@...ech.de>,
        <philipp.tomsich@...ll.eu>, <robh@...nel.org>, <maz@...nel.org>,
        <viresh.kumar@...aro.org>, <linux-riscv@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <Brice.Goglin@...ia.fr>
Subject: Re: [RFC 2/4] arch-topology: add a default implementation of
 store_cpu_topology()

On 08/07/2022 12:39, Sudeep Holla wrote:
> On Fri, Jul 08, 2022 at 12:03:41PM +0200, Greg KH wrote:
>> On Fri, Jul 08, 2022 at 10:47:10AM +0100, Sudeep Holla wrote:
>>> On Fri, Jul 08, 2022 at 11:28:19AM +0200, Geert Uytterhoeven wrote:
>>>> Hi Sudeep,
>>>>
>>>> On Fri, Jul 8, 2022 at 11:22 AM Sudeep Holla <sudeep.holla@....com> wrote:
>>>>> On Fri, Jul 08, 2022 at 08:35:57AM +0000, Conor.Dooley@...rochip.com wrote:
>>>>>> If you're okay with patch 1/4, I'll resubmit it as a standalone v2.
>>>>>>
>>>>>
>>>>> That would be great, thanks. You can most the code to move to generic from
>>>>> both arm64 and risc-v once we have this in v5.20-rc1
>>>>
>>>> Why not ignore risc-v for now, and move the arm64 implementation to
>>>> the generic code for v5.20, so every arch will have it at once?
>>>>
>>>
>>> We could but,
>>> 1. This arch_topology is new and has been going through lot of changes
>>>     recently and having code there might make it difficult to backport
>>>     changes that are required for RISC-V(my guess)
>>
>> Worry about future issues in the future.  Make it simple now as you know
>> what you are dealing with at the moment.
>>
> 
> Sure, I was just suggesting and expecting someone from RISC-V community or
> maintainers to make a call. As I said it is based on my understanding.
> hence I have mentioned as guess. So I am not against it as such.

I did a little bit of poking in the git history.
The last code touching the arm implementation was:
3102bc0e6ac7 ("arm64: topology: Stop using MPIDR for topology information")
on Fri Oct 2 12:01:41 2020 +0100

The introduction of arch-topology stuff to RISC-V was:
03f11f03dbfe ("RISC-V: Parse cpu topology during boot.")
on Thu Jun 27 12:53:00 2019 -0700

Backporting as far as v5.10 should be no real effort and I don't think
to v5.4 that should be meaninfully harder. If 3102bc0e6ac7 hasn't been
backported already, maybe it should be since it appears to have been
fixing a problem too.

Based on that, I think doing this the straightforward way in the first
place is a better idea.

I'll respin the series as:
patch 1: Move arm64 to the generic implementation
patch 2: Make RISC-V use the generic implementation

Thanks,
Conor.