Re: [Xen-devel] [RFC PATCH v1 01/10] xen/arm: make secondary gic init as notifier call

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sat, 2014-03-22 at 13:54 +0000, Julien Grall wrote:
> Hello Vijay,
> 
> On 22/03/14 08:32, Vijay Kilari wrote:
> > On Fri, Mar 21, 2014 at 10:45 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> 
> > wrote:
> >> On Wed, 2014-03-19 at 19:47 +0530, vijay.kilari@xxxxxxxxx wrote:
> >>> From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
> >>>
> >>> make gic init for secondary cpus as notifier call
> >>> instead calling directly from secondary boot for
> >>> each cpu.
> >>
> >>> This makes secondary gic init generic and runtime.
> >>
> >> s/and/at/ perhaps? Otherwise I can't make sense of what you are trying
> >> to say.
> >>
> >   OK, I will rephrase it.
> >>
> >>> +static struct notifier_block gic_cpu_nb = {
> >>> +    .notifier_call = gic_init_secondary_cpu,
> >>> +    .priority = 100
> >>>
> >> In wondering what 100 was, I notice that the other similar uses have a
> >> "/* Highest priority */" comment, please add one here too.
> >>
> >> I notice that the percpu stuff (cpu_percpu_nfb) is also priority == 100,
> >> which makes me suspect that they will run in arbitrary order, which
> >> makes me uncomfortable, not least because at least gic_{cpu,hyp}_init
> >> both touch per-cpu data structures.
> >>
> >> Ah, I see the percpu stuff is a CPU_UP_PREPARE notifier, so has already
> >> happened. Good. It does make me wonder if it is wise to do something as
> >> critical as interrupt controller setup in a notifier. Do you think this
> >> is necessary for some reason?
> >>
> >     Yes, I kept it at highest priority thinking that it is critical.
> >      from the comment in include/xen/cpu.h, CPU_STARTING suits because
> >      gic_{cpu,hyp}_init should run on new cpu.
> >
> >        /* CPU_STARTING: CPU nearly online. Runs on new CPU, irqs still
> > disabled. */
> >
> >      Is there any difference with Xen compared to kernel? that suggest me 
> > to use
> >      CPU_UP_PREPARE?
> 
> CPU_UP_PREPARE notifiers are called from the boot CPU. Here we want to 
> call GIC init on the newly booted CPU.
> 
> So CPU_STARTING is fine.

Yeah, thinking about it some more I think this is ok.

Ian.


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