Re: [PATCH v3 10/16] xen/arm: cpufeature: Provide an helper to check if a capability is supported

[Julien Grall <julien.grall@arm.com>]

Hi Stefano,

On 22/06/16 10:59, Stefano Stabellini wrote:
> On Tue, 7 Jun 2016, Julien Grall wrote:
>> The CPU capabilities will be set depending on the value found in the CPU
>> registers. This patch provides a generic to go through a set of capabilities
>> and find which one should be enabled.
>>
>> The parameter "info" is used to display the kind of capability updated (e.g
>> workaround, feature...).
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>>
>> ---
>>      Changes in v3:
>>           - Patch added. The code was previously part of "Detect
>>           silicon...".
>> ---
>>   xen/arch/arm/cpufeature.c        | 16 ++++++++++++++++
>>   xen/include/asm-arm/cpufeature.h |  9 +++++++++
>>   2 files changed, 25 insertions(+)
>>
>> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
>> index 7a1b56b..088625b 100644
>> --- a/xen/arch/arm/cpufeature.c
>> +++ b/xen/arch/arm/cpufeature.c
>> @@ -24,6 +24,22 @@
>>
>>   DECLARE_BITMAP(cpu_hwcaps, ARM_NCAPS);
>>
>> +void update_cpu_capabilities(const struct arm_cpu_capabilities *caps,
>> +                             const char *info)
>> +{
>> +    int i;
>> +
>> +    for ( i = 0; caps[i].matches; i++ )
>> +    {
>> +        if ( !caps[i].matches(&caps[i]) )
>> +            continue;
>> +
>> +        if ( !cpus_have_cap(caps[i].capability) && caps[i].desc )
>> +            printk(XENLOG_INFO "%s: %s\n", info, caps[i].desc);
>
> The patch is OK. I still have the same comment as before: if an info
> parameter is passed to this function with a string, then I think the
> string should contain some useful information. Not a generic message.

It is useful. As mentioned in the commit message the parameter "info" is 
used to display the kind of capability updated (e.g workaround, feature, 
...).

> I would just do:
>
>      printk(XENLOG_INFO "enable workaround for: %s\n", caps[i].desc);
>
> If one day we need to change the message depending on the caller, then
> that day we'll add a parameter to update_cpu_capabilities.

We both know that this function will be used for other purpose very 
soon. So I would rather avoid to modify again in the future. That is why 
I described the purpose in the commit message.

Cheers,

-- 
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel