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. -- Catalin
