linux-kernel - Re: [PATCH v2 16/20] arm64: Handle shared capability entries

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Message-ID: <fd750ccd-5f50-df9b-6ac0-8ddc86b76d0d@arm.com>
Date:   Thu, 8 Feb 2018 12:05:24 +0000
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, mark.rutland@....com,
        ckadabi@...eaurora.org, ard.biesheuvel@...aro.org,
        marc.zyngier@....com, catalin.marinas@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, jnair@...iumnetworks.com
Subject: Re: [PATCH v2 16/20] arm64: Handle shared capability entries

On 08/02/18 12:04, Dave Martin wrote:
> On Wed, Jan 31, 2018 at 06:28:03PM +0000, Suzuki K Poulose wrote:
>> Some capabilities have different criteria for detection and associated
>> actions based on the matching criteria, even though they all share the
>> same capability bit. So far we have used multiple entries with the same
>> capability bit to handle this. This is prone to errors, as the
>> cpu_enable is invoked for each entry, irrespective of whether the
>> detection rule applies to the CPU or not. And also this complicates
>> other helpers, e.g, __this_cpu_has_cap.
>>
>> This patch adds a wrapper entry to cover all the possible variations
>> of a capability and ensures :
>>   1) The capabilitiy is set when at least one of the entry detects
>>   2) Action is only taken for the entries that detects.
>>
>> This avoids explicit checks in the call backs. The only constraint
>> here is that, all the entries should have the same "type".
>>
>> Cc: Dave Martin <dave.martin@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
> 
> [...]
> 
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> 
> [...]
> 
>> @@ -1275,7 +1274,7 @@ static bool __verify_local_cpu_caps(const struct arm64_cpu_capabilities *caps_li
>>   		if (!(caps->type & scope_mask))
>>   			continue;
>>   
>> -		cpu_has_cap = __this_cpu_has_cap(caps_list, caps->capability);
>> +		cpu_has_cap = caps->matches(caps, SCOPE_LOCAL_CPU);
> 
> One other minor thing: the original caps_list argument seems no longer
> to be needed in this function after this change.
> 
> Can we rename the caps_list argument to "caps" and remove the local
> variable of the same name?

Sure, will do.

Suzuki