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

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Date:   Wed, 19 Jan 2022 12:14:23 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     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 1/13/22 5:17 PM, Arnd Bergmann wrote:
> 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.

IIUC the purpose here would be a quick CPU ID documentation reference check ?
I will wait for other opinions here and add the remaining in a separate patch
probably.

> 
>       Arnd
>