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

Anshuman Khandual
2023-08-11T10:26:30Z

On 8/11/23 15:42, Will Deacon wrote:
> On Fri, Aug 11, 2023 at 02:13:42PM +0530, Anshuman Khandual wrote:
>> On 8/8/23 13:52, Anshuman Khandual wrote:
>>> + /*
>>> + * 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;
>>> + }
>>> + }
>>
>> As discussed on the previous version i.e V3 thread, will move the
>> 'this_gsi' check after parse_gsi(), inside if (!gsi) conditional
>> block. This will treat subsequent cpu parse_gsi()'s failure as a
>> mismatch thus triggering the pr_warn() message.
>>
>> diff --git a/drivers/perf/arm_pmu_acpi.c b/drivers/perf/arm_pmu_acpi.c
>> index 845683ca7c64..6eae772d6298 100644
>> --- a/drivers/perf/arm_pmu_acpi.c
>> +++ b/drivers/perf/arm_pmu_acpi.c
>> @@ -98,11 +98,11 @@ arm_acpi_register_pmu_device(struct platform_device *pdev, u8 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) {
>> + if (!this_gsi)
>> + return 0;
>
> Why do you need this hunk?

Otherwise '0' gsi on all cpus would just clear the above homogeneity
test, and end up in acpi_register_gsi() making it fail, but with the
following warning before returning with -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;
}

Is this behaviour better than returning 0 after detecting '0' gsi in
the first cpu to avoid the above mentioned scenario ? Although 0 gsi
followed by non-zero ones will still end up warning about a mismatch.