Re: [PATCH v4] ARM: perf: save/restore pmu registers in pm notifier

[Sudeep Holla]

Hi Neil,

On 20/10/14 09:46, Neil Zhang wrote:
> > -----Original Message----- From: Will Deacon
> > [mailto:will.deacon@xxxxxxx] Sent: 2014年7月4日 1:57 To: Neil Zhang
> > Cc: Sudeep Holla; 'linux@xxxxxxxxxxxxxxxx'; 'linux-arm-
> > kernel@xxxxxxxxxxxxxxxxxxx'; 'linux-kernel@xxxxxxxxxxxxxxx';
> > 'devicetree@xxxxxxxxxxxxxxx' Subject: Re: [PATCH v4] ARM: perf:
> > save/restore pmu registers in pm notifier
> >
> > On Mon, Jun 30, 2014 at 11:39:15AM +0100, Neil Zhang wrote:
> > > > > > I will prepare another patch to add DT description under
> > > > > > PMU since there is no generic power domain support for pm
> > > > > > notifier if no other concerns. We can change the manner if
> > > > > > there is generic power domain support for pm notifier
> > > > > > later. Thanks.
> > > > >
> > > > > No, please don't add any DT bindings for power domains
> > > > > specific to PMU node. We can't change the DT bindings once
> > > > > added.
> > > > >
> > > > > As I pointed out the DT bindings for generic power domains
> > > > > are under discussion. See if you can reuse it, if not help in
> > > > > extending it so that it can be used.
> > > > Sorry for reply later. As I said before the under discussed
> > > > generic power domain is not suitable for CPU peripherals since
> > > >  they are all known belong to CPU or cluster power domain. If
> > > > we want to follow the way they are discussion, we need to
> > > > register core and cluster power provider, and need vfp/gic/pmu
> > > > etc to require them.
> > > > Is it really suitable?
> > > Do you have any comments? If no, I would like to put it under PMU
> > > node.
> >
> > Sudeep is a better person to comment than me, but I'd still rather
> >  this was handled more generically as opposed to a PMU-specific
> > hack. I don't see a problem including GIC and VFP here, but only
> > when we actually need to save/restore them (i.e. what the hardware
> >  guys went crazy with the power domains).
>
> Long time no follow up for this loop. Sorry that I will pick it
> again.
Yes, the generic PD got added in v3.18-rc1, it's better to check if we
can reuse it. I will also have a look at that and think about how we can
use it.

> Will, I prefer to check always-on field under PMU node to check
> whether we need Save/restore them.
But how do you handle it for different idle states. e.g. if CPU is in
retention, PMU's *might be* retained. Also I don't think PMUs will be
placed in "always-on" power domain like timers. So using "always-on"
sounds incorrect to me.

Regards,
Sudeep

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