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

From: Anders Roxell <anders.roxell@linaro.org>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] arm_pmu: Mark expected switch fall-through
Date: Tue, 30 Jul 2019 17:21:03 +0200	[thread overview]
Message-ID: <CADYN=9+9pUuMVwEw1_mgLsGMmB3Hm_EHr9vbwQZ_Axd7o9VFZw@mail.gmail.com> (raw)
In-Reply-To: <20190730124352.iwh5kbnc2d76mqyf@willie-the-truck>

On Tue, 30 Jul 2019 at 14:43, Will Deacon <will@kernel.org> wrote:
>
> On Tue, Jul 30, 2019 at 02:30:27PM +0200, Anders Roxell wrote:
> > On Tue, 30 Jul 2019 at 13:28, Will Deacon <will@kernel.org> wrote:
> > >
> > > On Tue, Jul 30, 2019 at 12:24:15PM +0100, Mark Rutland wrote:
> > > > 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@linaro.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@arm.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@arm.com>
> > >
> > > I gave up waiting
> >
> > I'm sorry for letting you wait.
>
> No, not at all. It's just that everybody was piling in with patches for
> these issues and I suspected you were busy dealing with responses. Rather
> than wait, I figured the best bet was just to get this fixed.

Thanks.

>
> Are you going to respin the SMMUv3 change per Robin's feedback?

Yes, just sent it.

Cheers,
Anders