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

Suzuki K Poulose
2023-08-09T12:55:33Z

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@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?

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.

>
>>> + 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).

>
>> 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.

Ok, fair point.

Suzuki

>
> Will