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

[Qais Yousef]

On 10/22/20 15:31, Catalin Marinas wrote:
> On Thu, Oct 22, 2020 at 03:55:59PM +0200, Greg Kroah-Hartman wrote:
> > 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...
> 
> I don't know what Qais thinks but a file matching the syntax of the
> present/online/offline/possible files (e.g. 0-3) would look more
> consistent.

Yes. Sorry I thought it's obvious.

Thanks

--
Qais Yousef