[PATCH] arm64: Add support for Half precision floating point

[Catalin Marinas]

On Tue, Jan 26, 2016 at 04:02:58PM +0000, Will Deacon wrote:
> On Tue, Jan 26, 2016 at 03:52:46PM +0000, Suzuki K Poulose wrote:
> > ARMv8.2 extensions [1] include an optional feature, which supports
> > half precision(16bit) floating point/asimd data processing
> > instructions. This patch adds support for detecting and exposing
> > the same to the userspace via HWCAPs
> > 
> > [1] https://community.arm.com/groups/processors/blog/2016/01/05/armv8-a-architecture-evolution
> > 
> > Signed-off-by: Suzuki K. Poulose <suzuki.poulose at arm.com>
> > ---
> >  arch/arm64/include/uapi/asm/hwcap.h |    2 ++
> >  arch/arm64/kernel/cpufeature.c      |    2 ++
> >  arch/arm64/kernel/cpuinfo.c         |    2 ++
> >  3 files changed, 6 insertions(+)
> > 
> > diff --git a/arch/arm64/include/uapi/asm/hwcap.h b/arch/arm64/include/uapi/asm/hwcap.h
> > index 361c8a8..a739287 100644
> > --- a/arch/arm64/include/uapi/asm/hwcap.h
> > +++ b/arch/arm64/include/uapi/asm/hwcap.h
> > @@ -28,5 +28,7 @@
> >  #define HWCAP_SHA2		(1 << 6)
> >  #define HWCAP_CRC32		(1 << 7)
> >  #define HWCAP_ATOMICS		(1 << 8)
> > +#define HWCAP_FPHP		(1 << 9)
> > +#define HWCAP_ASIMDHP		(1 << 10)
> 
> Where did we get to with the mrs trapping you proposed here?
> 
>   http://lists.infradead.org/pipermail/linux-arm-kernel/2015-October/374609.html
> 
> At some point, we need to consider whether or not we want to continue
> adding new HWCAPs or whether your suggestion above is actually useful
> to userspace.

IMO, even if we merge the MRS emulation, I would still like to see
HWCAPs exported. We are not short on bits yet (53 to go ;)).

> Did the libc guys get anywhere with a prototype? What do we need to do
> to make progress with it?

This investigation should indeed continue but I think it is orthogonal.

-- 
Catalin