[RFC PATCH v2 17/23] arm64/sve: In-kernel vector length availability query interface

[alex.bennee@linaro.org (Alex Bennée)]

Dave Martin <Dave.Martin@arm.com> writes:

> On Wed, Nov 21, 2018 at 04:16:42PM +0000, Alex Benn?e wrote:
>>
>> Dave Martin <Dave.Martin@arm.com> writes:
>>
>> > KVM will need to interrogate the set of SVE vector lengths
>> > available on the system.
>> >
>> > This patch exposes the relevant bits to the kernel, along with a
>> > sve_vq_available() helper to check whether a particular vector
>> > length is supported.
>> >
>> > vq_to_bit() and bit_to_vq() are not intended for use outside these
>> > functions, so they are given a __ prefix to warn people not to use
>> > them unless they really know what they are doing.
>>
>> Personally I wouldn't have bothered with the __ but whatever:
>>
>> Reviewed-by: Alex Benn?e <alex.bennee@linaro.org>
>
> OK, thanks
>
> I'll probably keep the __ unless somebody else objects, but if you feel
> strongly I could get rid of it.

nah - it's just a personal opinion...

> Perhaps I simply shouldn't have called attention to it in the commit
> message ;)

Psychological priming ;-)

>
> Cheers
> ---Dave
>
>>
>> >
>> > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
>> > ---
>> >  arch/arm64/include/asm/fpsimd.h | 29 +++++++++++++++++++++++++++++
>> >  arch/arm64/kernel/fpsimd.c      | 35 ++++++++---------------------------
>> >  2 files changed, 37 insertions(+), 27 deletions(-)
>> >
>> > diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
>> > index df7a143..ad6d2e4 100644
>> > --- a/arch/arm64/include/asm/fpsimd.h
>> > +++ b/arch/arm64/include/asm/fpsimd.h
>> > @@ -24,10 +24,13 @@
>> >
>> >  #ifndef __ASSEMBLY__
>> >
>> > +#include <linux/bitmap.h>
>> >  #include <linux/build_bug.h>
>> > +#include <linux/bug.h>
>> >  #include <linux/cache.h>
>> >  #include <linux/init.h>
>> >  #include <linux/stddef.h>
>> > +#include <linux/types.h>
>> >
>> >  #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
>> >  /* Masks for extracting the FPSR and FPCR from the FPSCR */
>> > @@ -89,6 +92,32 @@ extern u64 read_zcr_features(void);
>> >
>> >  extern int __ro_after_init sve_max_vl;
>> >  extern int __ro_after_init sve_max_virtualisable_vl;
>> > +/* Set of available vector lengths, as vq_to_bit(vq): */
>> > +extern __ro_after_init DECLARE_BITMAP(sve_vq_map, SVE_VQ_MAX);
>> > +
>> > +/*
>> > + * Helpers to translate bit indices in sve_vq_map to VQ values (and
>> > + * vice versa).  This allows find_next_bit() to be used to find the
>> > + * _maximum_ VQ not exceeding a certain value.
>> > + */
>> > +static inline unsigned int __vq_to_bit(unsigned int vq)
>> > +{
>> > +	return SVE_VQ_MAX - vq;
>> > +}
>> > +
>> > +static inline unsigned int __bit_to_vq(unsigned int bit)
>> > +{
>
> [...]


--
Alex Benn?e