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

[Julien Grall <julien.grall@xxxxxxx>]

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@xxxxxxx>
> >
> > ---
> >      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

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