Re: [PATCH V4 1/4] arm_pmu: acpi: Refactor arm_spe_acpi_register_device()

[Will Deacon <will@kernel.org>]

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@arm.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-kernel@vger.kernel.org
> > Co-developed-by: Will Deacon <will@kernel.org>
> > Signed-off-by: Will Deacon <will@kernel.org>
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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
> > @@ -69,6 +69,63 @@ static void arm_pmu_acpi_unregister_irq(int cpu)
> >   		acpi_unregister_gsi(gsi);
> >   }
> > +static int __maybe_unused
> > +arm_acpi_register_pmu_device(struct platform_device *pdev, u8 len,
> > +			     u16 (*parse_gsi)(struct acpi_madt_generic_interrupt *))
> > +{
> > +	int cpu, this_hetid, hetid, irq, ret;
> > +	u16 this_gsi, gsi = 0;
> > +
> > +	/*
> > +	 * Ensure that platform device must have IORESOURCE_IRQ
> > +	 * resource to hold gsi interrupt.
> > +	 */
> > +	if (pdev->num_resources != 1)
> > +		return -ENXIO;
> > +
> > +	if (pdev->resource[0].flags != IORESOURCE_IRQ)
> > +		return -ENXIO;
> > +
> > +	/*
> > +	 * Sanity check all the GICC tables for the same interrupt
> > +	 * number. For now, only support homogeneous ACPI machines.
> > +	 */
> > +	for_each_possible_cpu(cpu) {
> > +		struct acpi_madt_generic_interrupt *gicc;
> > +
> > +		gicc = acpi_cpu_get_madt_gicc(cpu);
> > +		if (gicc->header.length < len)
> > +			return gsi ? -ENXIO : 0;
> > +
> > +		this_gsi = parse_gsi(gicc);
> > +		if (!this_gsi)
> > +			return gsi ? -ENXIO : 0;
> > +
> > +		this_hetid = find_acpi_cpu_topology_hetero_id(cpu);
> > +		if (!gsi) {
> > +			hetid = this_hetid;
> > +			gsi = this_gsi;
> > +		} else if (hetid != this_hetid || gsi != this_gsi) {
> > +			pr_warn("ACPI: %s: must be homogeneous\n", pdev->name);
> > +			return -ENXIO;
> > +		}
> > +	}
> > +
> > +	irq = acpi_register_gsi(NULL, gsi, ACPI_LEVEL_SENSITIVE, ACPI_ACTIVE_HIGH);
> > +	if (irq < 0) {
> > +		pr_warn("ACPI: %s Unable to register interrupt: %d\n", pdev->name, gsi);
> > +		return -ENXIO;
> > +	}
> > +
> > +	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?

> > +	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?
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.

> Could we not drop the above message as all the other possible error
> scenarios are reported. We could simply make the above helper void, see my
> comment above.

I disagree. If the ACPI tables are borked, we should print a message saying
so.

Will

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