linux-kernel - RE: [PATCH v4] ARM: perf: save/restore pmu registers in pm notifier

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Message-ID: <175CCF5F49938B4D99B2E3EF7F558EBE5507A3C1F1@SC-VEXCH4.marvell.com>
Date:	Tue, 29 Apr 2014 19:21:22 -0700
From:	Neil Zhang <zhangwm@...vell.com>
To:	Will Deacon <will.deacon@....com>
CC:	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH v4] ARM: perf: save/restore pmu registers in pm notifier


> -----Original Message-----
> From: Will Deacon [mailto:will.deacon@....com]
> Sent: 2014年4月24日 1:08
> To: Neil Zhang
> Cc: linux@....linux.org.uk; linux-arm-kernel@...ts.infradead.org;
> linux-kernel@...r.kernel.org; Sudeep Holla; devicetree@...r.kernel.org
> Subject: Re: [PATCH v4] ARM: perf: save/restore pmu registers in pm notifier
> 
> On Wed, Apr 23, 2014 at 11:31:09AM +0100, Neil Zhang wrote:
> >
> > > -----Original Message-----
> > > From: Will Deacon [mailto:will.deacon@....com]
> > > Sent: 2014年4月22日 18:37
> > > To: Neil Zhang
> > > Cc: linux@....linux.org.uk; linux-arm-kernel@...ts.infradead.org;
> > > linux-kernel@...r.kernel.org; Sudeep Holla;
> > > devicetree@...r.kernel.org
> > > Subject: Re: [PATCH v4] ARM: perf: save/restore pmu registers in pm
> > > notifier
> > >
> > > Hi Neil,
> > >
> > > On Tue, Apr 22, 2014 at 03:26:36AM +0100, Neil Zhang wrote:
> > > > This adds core support for saving and restoring CPU PMU registers
> > > > for suspend/resume support i.e. deeper C-states in cpuidle terms.
> > > > This patch adds support only to ARMv7 PMU registers save/restore.
> > > > It needs to be extended to xscale and ARMv6 if needed.
> > > >
> > > > I made this patch because DS-5 is not working on Marvell's CA7 based
> SoCs.
> > > > And it has consulted Sudeep KarkadaNagesha's patch set for multiple
> PMUs.
> > > >
> > > > Thanks Will and Sudeep's suggestion to only save / restore used events.
> > >
> > > Whilst this is a step in the right direction, I'd still like to see
> > > the save/restore predicated on something in the device-tree or
> > > otherwise. Most SoCs *don't* require these registers to be preserved
> > > by software, so we need a way to describe that the PMU is in a
> > > power-domain where its state is lost when the CPU goes idle.
> > >
> > > This doesn't sound like a PMU-specific problem, so there's a
> > > possibility that this has been discussed elsewhere, in the context
> > > of other IP blocks
> > >
> > > [adding the devicetree list in case somebody there is aware of any
> > > work in this area]
> > >
> >
> > Thanks Will.
> > What should I do now?
> > Add a filed under PMU or waiting for somebody whether there are
> > general supporting for power domain maintain.
> 
> I think we need some input from the device-tree guys to see whether they
> would object to us solving this locally (in the PMU node) or not.
> Personally, I'd much prefer a general way to describe the need for pm-notifiers,
> but if that's not being looked at then we can cook something specifically for
> our needs.
> 

No input from device-tree guys :(

> Will

Best Regards,
Neil Zhang