Re: [Xen-devel] [PATCH] xen/arm: remove check for generic timer support for arm64

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-06-02 at 14:23 +0100, Julien Grall wrote:
> On 06/02/2014 02:03 PM, Ian Campbell wrote:
> > On Mon, 2014-06-02 at 12:13 +0100, Julien Grall wrote:
> >> On 06/02/2014 12:09 PM, Ian Campbell wrote:
> >>> On Mon, 2014-06-02 at 14:07 +0530, vijay.kilari@xxxxxxxxx wrote:
> >>>> From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
> >>>>
> >>>> arm64 always supports generic timer. So check is not required
> >>>> for arm64. For platforms which supports only aarch64 mode this
> >>>> check always passes and panics
> >>>
> >>> Ah, because the relevant feature flag/register is 32-bit only.
> >>>
> >>> I'd prefer to see this done in the cpufeature header as:
> >>>         #ifdef CONFIG_ARM_32
> >>>         #define cpu_has_gentimer  (boot_cpu_feature32(gentimer) == 1)
> >>>         #else
> >>>         #define cpu_has_gentimer  (1)
> >>>         #endif
> >>> rather than adding #ifdef to the common code. Likewise for any similar
> >>> "always on for aarch64" features.
> >>
> >> AFAIU, the feature flag exists on ARMv8 platform with aarch32 support.
> >> So an ifdef may not be the correct solution here.
> > 
> > The flag might exist in the AArch32 feature registers (for compat with
> > v7) but AIUI the feature is not actually optional on v8.
> 
> The manual says the ARM Generic Timer is an optional extension to an
> ARMv8 implementation.

So it does. In that case cpu_has_gentimer should turn into a check of
ID_PFR1_EL1.GenTimer for arm64 builds.

Ian.


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