Re: [PATCH] tune-cortexa72-cortexa53: Add tune

[Adrian Bunk <bunk@stusta.de>]

On Fri, Dec 13, 2019 at 06:47:33PM -0600, Joshua Watt wrote:
> On Fri, Dec 13, 2019 at 5:10 PM Adrian Bunk <bunk@stusta.de> wrote:
> >
> > On Fri, Dec 13, 2019 at 04:03:09PM -0600, Joshua Watt wrote:
> > > Adds a tune for Cortex-A72 Cortex-A53 big.LITTLE SoCs, e.g.  Rockchip
> > > RK3399
> > >...
> > > +TUNE_FEATURES_tune-cortexa72-cortexa53 = "${TUNE_FEATURES_tune-aarch64} cortexa72-cortexa53"
> > >...
> >
> > Looking at the gcc sources cortexa72-cortexa53 defaults to crc enabled,
> > so TUNE_FEATURES_tune-cortexa72-cortexa53 must contain crc.
> 
> I think that's armv8.1-a, the cortex A72 is only armv8-a (at least
> AFAICT), so I think crc would still be an optional feature.
>...

It is optional for armv8-a, but not for Cortex A53 or A72.

What matters in practice is that gcc automatically enables it for 
cortex-a72.cortex-a53, so the resulting code might not run on
armv8-a hardware without support for crc - things will break
if the tune features are not 100% aligned with whatever gcc
is doing.

cu
Adrian