[PATCH] arch/powerpc: advertise ISA2.07, HTM, DSCR, EBB and ISEL bits in HWCAP2

[Ryan Arnold]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 05/06/2013
04:37:08 PM:

> Benjamin Herrenschmidt <benh at kernel.crashing.org>
> 05/06/2013 04:37 PM
>
> To
>
> Ryan Arnold/Rochester/IBM at IBMUS
>
> cc
>
> Nishanth Aravamudan <nacc at linux.vnet.ibm.com>, linuxppc-
> dev at lists.ozlabs.org, Michael R Meissner/Cambridge/IBM at IBMUS,
> Michael Neuling <michael.neuling at au1.ibm.com>, Peter Bergner/
> Rochester/IBM at IBMUS, Steve Munroe/Rochester/IBM at IBMUS
>
> Subject
>
> Re: [PATCH] arch/powerpc: advertise ISA2.07, HTM, DSCR, EBB and ISEL
> bits in HWCAP2
>
> On Mon, 2013-05-06 at 09:38 -0500, Ryan Arnold wrote:
> > My understanding was that these bits being 'on' is an indication of
> > what features the hardware supports (or what the kernel emulates) and
> > a not an indication of whether that facility is currently enabled or
> > not.  If the hardware supports a particular feature but it is not
> > enabled I'd expect that user-space usage of that feature would cause
> > the kernel to trap on a facility availability exception (which is how
> > Altivec/VMX is implemented, being defaulted to turned off).
>
> Right but the discussion is about whether we should expose the bits
> when the kernel doesn't have the ability to handle the feature :-)
>
> IE. We need to remove the HTM feature if the kernel is compiled without
> transactional memory support.

Thanks for explaining. This is exactly how it should work.

Ryan
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