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

[Adrian Bunk <bunk@stusta.de>]

On Fri, Dec 13, 2019 at 07:28:28PM -0600, Joshua Watt wrote:
> On Fri, Dec 13, 2019, 7:22 PM Adrian Bunk <bunk@stusta.de> wrote:
> 
> > 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.
> 
> I agree, but I can't find anywhere that says crc is enabled by default when
> the tune is cortexa72.cortexa53. Maybe I'm looking in the wrong location?

https://github.com/gcc-mirror/gcc/blob/master/gcc/config/arm/arm-cpus.in#L1278

> Thanks

cu
Adrian