linux-kernel - Re: [PATCH] arm_pmu: Mark expected switch fall-through

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Message-ID: <20190730112415.GB51922@lakrids.cambridge.arm.com>
Date:   Tue, 30 Jul 2019 12:24:15 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     Anders Roxell <anders.roxell@...aro.org>, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm_pmu: Mark expected switch fall-through

On Fri, Jul 26, 2019 at 04:18:25PM +0100, Lorenzo Pieralisi wrote:
> On Fri, Jul 26, 2019 at 01:29:56PM +0100, Mark Rutland wrote:
> > On Fri, Jul 26, 2019 at 01:27:37PM +0200, Anders Roxell wrote:
> > > When fall-through warnings was enabled by default the following warning
> > > was starting to show up:
> > > 
> > > ../drivers/perf/arm_pmu.c: In function ‘cpu_pm_pmu_notify’:
> > > ../drivers/perf/arm_pmu.c:726:3: warning: this statement may fall
> > >  through [-Wimplicit-fallthrough=]
> > >    cpu_pm_pmu_setup(armpmu, cmd);
> > >    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > ../drivers/perf/arm_pmu.c:727:2: note: here
> > >   case CPU_PM_ENTER_FAILED:
> > >   ^~~~
> > > 
> > > Rework so that the compiler doesn't warn about fall-through.
> > > 
> > > Fixes: d93512ef0f0e ("Makefile: Globally enable fall-through warning")
> > > Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> > > ---
> > > 
> > > I'm not convinced that this is the correct patch to fix this issue.
> > > However, I can't see why we do 'armpmu->start(armpmu);' only in 'case
> > > CPU_PM_ENTER_FAILED' and why we not call function cpu_pm_pmu_setup()
> > > there also, since in cpu_pm_pmu_setup() has a case prepared for
> > > CPU_PM_ENTER_FAILED.
> > 
> > I agree, think that should be:
> > 
> > 	case CPU_PM_EXIT:
> > 	case CPU_PM_ENTER_FAILED:
> > 		cpu_pm_pmu_setup(armpmu, cmd);
> > 		armpmu->start(armpmu);
> > 		break;
> > 
> > ... so that we re-start the events before we start the PMU.
> > 
> > That would be a fix for commit:
> > 
> >   da4e4f18afe0f372 ("drivers/perf: arm_pmu: implement CPU_PM notifier")
> 
> Yes that's correct, apologies. Probably we did not hit it because CPU PM
> notifier entry failures are a pretty rare event; regardless:
> 
> Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> 
> I can send the updated fix, just let me know.

I'm not sure what Will wants, but assuming you do so:

Acked-by: Mark Rutland <mark.rutland@....com>

Thanks,
Mark.