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Subject: Re: [RFT PATCH v1 0/4] Unify CPU topology across ARM64 & RISC-V
To:     Morten Rasmussen <morten.rasmussen@arm.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Anup Patel <anup@brainfault.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Dmitriy Cherkasov <dmitriy@oss-tech.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        Jeremy Linton <jeremy.linton@arm.com>,
        Juri Lelli <juri.lelli@arm.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will.deacon@arm.com>
References: <1543534100-3654-1-git-send-email-atish.patra@wdc.com>
 <20181207134509.GA5913@e105550-lin.cambridge.arm.com>
From:   Atish Patra <atish.patra@wdc.com>
Message-ID: <dffd0d6e-bebe-ae31-548b-1778d08a3285@wdc.com>
Date:   Mon, 10 Dec 2018 16:11:21 -0800
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On 12/7/18 5:45 AM, Morten Rasmussen wrote:
> Hi,
> 
> On Thu, Nov 29, 2018 at 03:28:16PM -0800, Atish Patra wrote:
>> The cpu-map DT entry in ARM64 can describe the CPU topology in
>> much better way compared to other existing approaches. RISC-V can
>> easily adopt this binding to represent it's own CPU topology.
>> Thus, both cpu-map DT binding and topology parsing code can be
>> moved to a common location so that RISC-V or any other
>> architecture can leverage that.
>>
>> The relevant discussion regarding unifying cpu topology can be
>> found in [1].
>>
>> arch_topology seems to be a perfect place to move the common
>> code. I have not introduced any functional changes in the moved
>> code. The only downside in this approach is that the capacity
>> code will be executed for RISC-V as well. But, it will exit
>> immediately after not able to find the appropriate DT node. If
>> the overhead is considered too much, we can always compile out
>> capacity related functions under a different config for the
>> architectures that do not support them.
>>
>> The patches have been tested for RISC-V and compile tested for
>> ARM64 & x86.
> 
> The cpu-map bindings are used for arch/arm too, and so is
> arch_topology.c. In fact, it was introduced to allow code-sharing
> between arm and arm64. Applying patch three breaks arm.
> 
> Moving the DT parsing to arch_topology.c we have to unify all three
> architectures. Be aware that arm and arm64 have some differences in how
> they detect cpu capacities. I think we might have to look at the split
> of code between arch/* and arch_topology.c again :-/
> 
> Morten
> 
Thank you for bringing this up. I will send a new version and make sure 
that it works on arm32 as well.


Regards,
Atish