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

[Nishanth Aravamudan <nacc@linux.vnet.ibm.com>]

On 04.05.2013 [09:23:51 +1000], Benjamin Herrenschmidt wrote:
> On Fri, 2013-05-03 at 16:19 -0700, Nishanth Aravamudan wrote:
> > +/* in AT_HWCAP2 */
> > +#define PPC_FEATURE2_ARCH_2_07         0x80000000
> > +#define PPC_FEATURE2_HTM               0x40000000
> > +#define PPC_FEATURE2_DSCR              0x20000000
> > +#define PPC_FEATURE2_EBB               0x10000000
> > +#define PPC_FEATURE2_ISEL              0x08000000
> 
> Should we "adjust" (ie filter out) some of these based
> on CONFIG_ options (such as transactional memory enabled,
> EBB supported by the hypervisor, etc...) ?

Err, yeah, that seems reasonable :) However, it seems like glibc uses
these values rather directly so it knows what bits to check for each
feature. Therefore, it seems like it would be better to do the
ifdeffery/checking in the user in cputable.c, but that seems like it
could get quite complicated.

Would it be ok (I guess I'm asking Ryan & co. here) to have an #ifdef in
the definition that may or may not mean the bit is set in the aux
vector, but the bit, if set, would always be the same bit?

-Nish