linux-kernel - Re: [PATCH v3 1/7] arm64/sysreg: Convert CCSIDR

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Message-ID: <1ef32b0c-6cee-75f7-e1e0-ede1f5b9a016@daynix.com>
Date:   Sun, 18 Dec 2022 20:35:12 +0900
From:   Akihiko Odaki <akihiko.odaki@...nix.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        James Morse <james.morse@....com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        asahi@...ts.linux.dev, Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Sven Peter <sven@...npeter.dev>,
        Hector Martin <marcan@...can.st>
Subject: Re: [PATCH v3 1/7] arm64/sysreg: Convert CCSIDR_EL1 to automatic
 generation

On 2022/12/18 20:23, Marc Zyngier wrote:
> On Sun, 18 Dec 2022 05:14:06 +0000,
> Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
>>
>> Convert CCSIDR_EL1 to automatic generation as per DDI0487I.a. The field
>> definition is for case when FEAT_CCIDX is not implemented. Fields WT,
>> WB, RA and WA are defined as per A.j since they are now reserved and
>> may have UNKNOWN values in I.a, which the file format cannot represent.
>>
>> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
>> ---
>>   arch/arm64/include/asm/sysreg.h |  1 -
>>   arch/arm64/tools/sysreg         | 11 +++++++++++
>>   2 files changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
>> index 7d301700d1a9..910e960661d3 100644
>> --- a/arch/arm64/include/asm/sysreg.h
>> +++ b/arch/arm64/include/asm/sysreg.h
>> @@ -425,7 +425,6 @@
>>   
>>   #define SYS_CNTKCTL_EL1			sys_reg(3, 0, 14, 1, 0)
>>   
>> -#define SYS_CCSIDR_EL1			sys_reg(3, 1, 0, 0, 0)
>>   #define SYS_AIDR_EL1			sys_reg(3, 1, 0, 0, 7)
>>   
>>   #define SYS_RNDR_EL0			sys_reg(3, 3, 2, 4, 0)
>> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
>> index 384757a7eda9..acc79b5ccf92 100644
>> --- a/arch/arm64/tools/sysreg
>> +++ b/arch/arm64/tools/sysreg
>> @@ -871,6 +871,17 @@ Sysreg	SCXTNUM_EL1	3	0	13	0	7
>>   Field	63:0	SoftwareContextNumber
>>   EndSysreg
>>   
>> +Sysreg	CCSIDR_EL1	3	1	0	0	0
>> +Res0	63:32
>> +Field	31:31	WT
>> +Field	30:30	WB
>> +Field	29:29	RA
>> +Field	28:28	WA
> 
> For fields described as a single bit, the tool supports simply
> indicating the bit number (28 rather than 28:28).
> 
> However, I strongly recommend against describing fields that have been
> dropped from the architecture.  This only happens when these fields
> are never used by any implementation, so describing them is at best
> useless.

arch/arm64/tools/gen-sysreg.awk does not allow a hole and requires all 
bits are described hence these descriptions. If you have an alternative 
idea I'd like to hear.

> 
>> +Field	27:13	NumSets
>> +Field	12:3	Associavity
>> +Field	2:0	LineSize
>> +EndSysreg
>> +
> 
> I don't think we have a good solution for overlapping fields that
> depend on other factors, either contextual (such as a mode that
> changes the layout of a sysreg), or architecture warts such as
> FEAT_CCIDX (which changes the layout of a well-known sysreg).
> 
> At least, put a comment here that indicates the context of the
> description.

Sounds good. I'll do so with the next version.

Regards,
Akihiko Odaki

> 
> Thanks,
> 
> 	M.
>