linux-kernel - Re: [PATCH] arm64: errata: Enable the AC03_CPU

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Message-ID: <314b8893-2ffd-4148-974b-725cfaa97d18@arm.com>
Date: Tue, 27 Aug 2024 07:22:16 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Oliver Upton <oliver.upton@...ux.dev>,
 D Scott Phillips <scott@...amperecomputing.com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Jonathan Corbet <corbet@....net>, Mark Rutland <mark.rutland@....com>,
 linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
 Besar Wicaksono <bwicaksono@...dia.com>,
 Easwar Hariharan <eahariha@...ux.microsoft.com>,
 Rob Herring <robh@...nel.org>, Andre Przywara <andre.przywara@....com>,
 linux-kernel@...r.kernel.org, patches@...erecomputing.com
Subject: Re: [PATCH] arm64: errata: Enable the AC03_CPU_38 workaround for
 ampere1a

On 8/27/24 04:53, Oliver Upton wrote:
> Hi D Scott,
> 
> On Mon, Aug 26, 2024 at 02:59:33PM -0700, D Scott Phillips wrote:
>> The ampere1a cpu is affected by erratum AC04_CPU_10 which is the same
>> bug as AC03_CPU38. Add ampere1a to the AC03_CPU_38 workaround midr list.
>>
>> Signed-off-by: D Scott Phillips <scott@...amperecomputing.com>
>> ---
>>  Documentation/arch/arm64/silicon-errata.rst | 2 ++
>>  arch/arm64/Kconfig                          | 2 +-
>>  arch/arm64/include/asm/cputype.h            | 2 ++
>>  arch/arm64/kernel/cpu_errata.c              | 1 +
>>  4 files changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst
>> index 50327c05be8d1..39c52385f11fb 100644
>> --- a/Documentation/arch/arm64/silicon-errata.rst
>> +++ b/Documentation/arch/arm64/silicon-errata.rst
>> @@ -55,6 +55,8 @@ stable kernels.
>>  +----------------+-----------------+-----------------+-----------------------------+
>>  | Ampere         | AmpereOne       | AC03_CPU_38     | AMPERE_ERRATUM_AC03_CPU_38  |
>>  +----------------+-----------------+-----------------+-----------------------------+
>> +| Ampere         | AmpereOne AC04  | AC04_CPU_10     | AMPERE_ERRATUM_AC03_CPU_38  |
>> ++----------------+-----------------+-----------------+-----------------------------+
> 
> We tend to stick the marketing term for a part in the second column so
> it is more recognizable for the user. Is this a placeholder for something
> different from "ampere1a"?

Agreed, even the MIDR being added here is for AMPERE1A. Probably something
like 'AmpereOneA' might be more suitable.

> 
>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
>> index f6b6b45073571..748aa536446ae 100644
>> --- a/arch/arm64/kernel/cpu_errata.c
>> +++ b/arch/arm64/kernel/cpu_errata.c
>> @@ -773,6 +773,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
>>  		.desc = "AmpereOne erratum AC03_CPU_38",
>>  		.capability = ARM64_WORKAROUND_AMPERE_AC03_CPU_38,
>>  		ERRATA_MIDR_ALL_VERSIONS(MIDR_AMPERE1),
>> +		ERRATA_MIDR_ALL_VERSIONS(MIDR_AMPERE1A),
> 
> This will break the workaround on AC03, since the second macro reassigns
> ::midr_range.
> 
> You'll want to use ERRATA_MIDR_RANGE_LIST() instead w/ an array of
> affected MIDRs.
> 

+1

Although ERRATA_MIDR_RANGE_LIST() in turn creates such a list.