Re: [RFC 2/4] arch-topology: add a default implementation of store_cpu_topology()

From: <Conor.Dooley@microchip.com>
To: <sudeep.holla@arm.com>, <gregkh@linuxfoundation.org>
Cc: <geert@linux-m68k.org>, <Conor.Dooley@microchip.com>,
	<paul.walmsley@sifive.com>, <palmer@dabbelt.com>,
	<palmer@rivosinc.com>, <aou@eecs.berkeley.edu>,
	<catalin.marinas@arm.com>, <will@kernel.org>, <rafael@kernel.org>,
	<Daire.McNamara@microchip.com>, <niklas.cassel@wdc.com>,
	<damien.lemoal@opensource.wdc.com>, <zong.li@sifive.com>,
	<kernel@esmil.dk>, <hahnjo@hahnjo.de>, <guoren@kernel.org>,
	<anup@brainfault.org>, <atishp@atishpatra.org>,
	<changbin.du@intel.com>, <heiko@sntech.de>,
	<philipp.tomsich@vrull.eu>, <robh@kernel.org>, <maz@kernel.org>,
	<viresh.kumar@linaro.org>, <linux-riscv@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>, <Brice.Goglin@inria.fr>
Subject: Re: [RFC 2/4] arch-topology: add a default implementation of store_cpu_topology()
Date: Fri, 8 Jul 2022 11:57:05 +0000	[thread overview]
Message-ID: <9f8d4e4d-f24b-faf3-687f-90370939c72f@microchip.com> (raw)
In-Reply-To: <20220708113915.ui77mgqckjzalwlh@bogus>

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@arm.com> wrote:
>>>>> On Fri, Jul 08, 2022 at 08:35:57AM +0000, Conor.Dooley@microchip.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.
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