linux-kernel - Re: [PATCH V4 1/4] arm_pmu: acpi: Refactor arm_spe_acpi_register

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Message-ID: <20230811101925.GB6827@willie-the-truck>
Date:   Fri, 11 Aug 2023 11:19:25 +0100
From:   Will Deacon <will@...nel.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org, yangyicong@...wei.com,
        Sami Mujawar <sami.mujawar@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        James Clark <james.clark@....com>, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 1/4] arm_pmu: acpi: Refactor
 arm_spe_acpi_register_device()

On Wed, Aug 09, 2023 at 01:54:55PM +0100, Suzuki K Poulose wrote:
> On 08/08/2023 14:16, Will Deacon wrote:
> > On Tue, Aug 08, 2023 at 09:48:16AM +0100, Suzuki K Poulose wrote:
> > > On 08/08/2023 09:22, Anshuman Khandual wrote:
> > > > Sanity checking all the GICC tables for same interrupt number, and ensuring
> > > > a homogeneous ACPI based machine, could be used for other platform devices
> > > > as well. Hence this refactors arm_spe_acpi_register_device() into a common
> > > > helper arm_acpi_register_pmu_device().
> > > > 
> > > > Cc: Catalin Marinas <catalin.marinas@....com>
> > > > Cc: Will Deacon <will@...nel.org>
> > > > Cc: Mark Rutland <mark.rutland@....com>
> > > > Cc: linux-arm-kernel@...ts.infradead.org
> > > > Cc: linux-kernel@...r.kernel.org
> > > > Co-developed-by: Will Deacon <will@...nel.org>
> > > > Signed-off-by: Will Deacon <will@...nel.org>
> > > > Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> > > > ---
> > > >    drivers/perf/arm_pmu_acpi.c | 105 ++++++++++++++++++++++--------------
> > > >    1 file changed, 65 insertions(+), 40 deletions(-)
> > > > 
> > > > diff --git a/drivers/perf/arm_pmu_acpi.c b/drivers/perf/arm_pmu_acpi.c
> > > > index 90815ad762eb..72454bef2a70 100644
> > > > --- a/drivers/perf/arm_pmu_acpi.c
> > > > +++ b/drivers/perf/arm_pmu_acpi.c
> > > > +	pdev->resource[0].start = irq;
> > > > +	ret = platform_device_register(pdev);
> > > > +	if (ret < 0) {
> > > > +		pr_warn("ACPI: %s: Unable to register device\n", pdev->name);
> > > > +		acpi_unregister_gsi(gsi);
> > > > +	}
> > > > +	return ret;
> > > 
> > > A postivie return value here could confuse the caller. Also, with my comment
> > > below, we don't really need to return something from here.
> > 
> > How does this return a positive value?
> 
> Right now, there aren't. My point is this function returns a "return value"
> of another function. And the caller of this function doesn't
> really follow the "check" it needs.  e.g.:
> 
> ret = foo();
> if (ret < 0)
> 	error;
> return ret;
> 
> 
> 
> And the caller only checks for
> 
> if (ret)
> 	error;
> 
> This seems fragile.

Yeah, the '< 0' check is weird. I'd be inclined to drop that entirely
from the helper function tbh...

> > > > +	int ret = arm_acpi_register_pmu_device(&spe_dev, ACPI_MADT_GICC_SPE,
> > > > +					       arm_spe_parse_gsi);
> > > > +	if (ret)
> > > >    		pr_warn("ACPI: SPE: Unable to register device\n");
> > > 
> > > With this change, a system without SPE interrupt description always
> > > generates the above message. Is this intended ?
> > 
> > If there are no irqs, why doesn't this return 0?
> 
> Apologies, I missed that.
> 
> > arm_acpi_register_pmu_device() should only fail if either:
> > 
> >    - The static resources passed in are broken
> >    - The tables are not homogeneous
> >    - We fail to register the interrupt
> > 
> > so something is amiss.
> 
> Agreed. We don't need duplicate messages about an error ?
> i.e., one in arm_acpi_register_pmu_device() and another
> one in the caller ? (Of course adding any missing error msgs).

... and then just print the registration failure message in the caller.

Will