[PATCH 2/6] arm64: Allow mismatched 32-bit EL0 support

[Will Deacon]

On Fri, Nov 06, 2020 at 02:48:35PM +0000, Qais Yousef wrote:
> On 11/06/20 13:00, Will Deacon wrote:
> > On Fri, Nov 06, 2020 at 12:54:25PM +0000, Qais Yousef wrote:
> > > FWIW I have my v3 over here in case it's of any help. It solves the problem of
> > > HWCAP discovery when late AArch32 CPU is booted by populating boot_cpu_date
> > > with 32bit features then.
> > > 
> > > 	git clone https://git.gitlab.arm.com/linux-arm/linux-qy.git -b asym-aarch32-upstream-v3 origin/asym-aarch32-upstream-v3
> > 
> > Cheers, I've done something similar. I was hoping to post it today, but I've
> > been side-tracked with bug fixing this morning. The main headache I ended up
> > with was allowing late-onlining of 64-bit-only CPUs if all the boot CPUs
> > are 32-bit capable. What do you do in that case?
> 
> Do you mean if CPUs 0-3 were 32bit capable and we boot with maxcpus=4 then
> attempt to bring the remaining 64bit-only cpus online later?

Right. I think we will refuse to online them. I'll post my attempt at
handling that shortly.

> Haven't tried that tbh. What symptoms do you expect to see? I can try it out.
> I'm off for the remainder of the day, but can spend few mins to run an
> experiment for sure.

No probs; I've been taking Friday afternoons off to burn holiday anyway, so
you didn't miss anything!

Will