linux-kernel - Re: [PATCH 1/2] arm64: Add Cortex-X2 CPU part definition

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Message-ID: <CAK8P3a2Q+iN1O6FEdUJRt=0bQu=6fkWAD3RCECfdhu4DKHq0pg@mail.gmail.com>
Date:   Thu, 13 Jan 2022 12:47:34 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki Poulose <suzuki.poulose@....com>,
        coresight@...ts.linaro.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] arm64: Add Cortex-X2 CPU part definition

On Thu, Jan 13, 2022 at 4:03 AM Anshuman Khandual
<anshuman.khandual@....com> wrote:
> On 1/12/22 4:20 PM, Arnd Bergmann wrote:
> > On Wed, Jan 12, 2022 at 10:34 AM Anshuman Khandual <anshuman.khandual@....com> wrote:
> >> Add the CPU Partnumbers for the new Arm designs.
> >> @@ -74,6 +74,7 @@
> >>  #define ARM_CPU_PART_NEOVERSE_N1       0xD0C
> >>  #define ARM_CPU_PART_CORTEX_A77                0xD0D
> >>  #define ARM_CPU_PART_CORTEX_A710       0xD47
> >> +#define ARM_CPU_PART_CORTEX_X2         0xD48
> >>  #define ARM_CPU_PART_NEOVERSE_N2       0xD49
> >
> > No objections to the patch, but would it be possible to just add all the missing
> > ones here to the degree that they are known already? I don't see any entries for
> > Cortex-A34, Cortex-A65AE, Cortex-A78, Cortex-A78C, Cortex-A78AE,
> > Neoverse-E1, Neoverse-V1, Cortex-X1, Cortex-X2, Cortex-A510, Cortex-A710
> > and Cortex-R82 among the Arm-designed cores that can run Linux, and there
> > are probably others that I missed going through the list.
>
> Hi Arnd,
>
> IIUC the part numbers are enumerated here only if there is an errata
> applicable for them which needs to be detected at boot. I am not sure
> whether all cpu versions that can run Linux, needs to be defined here.
> But then I might be missing something.

They clearly don't need to be defined here, and for other constants such
as the system registers we may not want to list them all, but I think for
the CPU IDs it makes sense to just list them all here rather than adding
them one at a time, as we tend to need them sooner or later anyway.

It also helps me personally to have a known place to look up the names
by value rather than chasing through reference manuals.

      Arnd