Re: [RFC PATCH v2 4/4] arm64: Export id_aar64fpr0 via sysfs

Greg Kroah-Hartman
2020-10-22T13:56:44Z

On Thu, Oct 22, 2020 at 02:47:52PM +0100, Qais Yousef wrote:
> On 10/21/20 15:41, Will Deacon wrote:
> > > We already expose MIDR and REVIDR via the current sysfs interface. We
> > > can expand it to include _all_ the other ID_* regs currently available
> > > to user via the MRS emulation and we won't have to debate what a new
> > > interface would look like. The MRS emulation and the sysfs info should
> > > probably match, though that means we need to expose the
> > > ID_AA64PFR0_EL1.EL0 field which we currently don't.
> > >
> > > I do agree that an AArch32 cpumask is an easier option both from the
> > > kernel implementation perspective and from the application usability
> > > one, though not as easy as automatic task placement by the scheduler (my
> > > first preference, followed by the id_* regs and the aarch32 mask, though
> > > not a strong preference for any).
> >
> > If a cpumask is easier to implement and easier to use, then I think that's
> > what we should do. It's also then dead easy to disable if necessary by
> > just returning 0. The only alternative I would prefer is not having to
> > expose this information altogether, but I'm not sure that figuring this
> > out from MIDR/REVIDR alone is reliable.
>
> So the mask idea is about adding a new
>
> /sys/devices/system/cpu/aarch32_cpus
>
> ?

Is this a file, a directory, or what? What's the contents?

Without any of that, I have no idea if it's "ok" or not...

thanks,

greg k-h