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

Anshuman Khandual
2023-08-16T06:31:22Z

On 8/11/23 16:30, Will Deacon wrote:
> On Fri, Aug 11, 2023 at 03:55:43PM +0530, Anshuman Khandual wrote:
>>
>>
>> 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;
>> }
>
> Ah gotcha, thanks.
>
>> 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.
>
> Can we move the check _after_ the loop, then? That way, we still detect
> mismatches but we'll quietly return 0 if nobody has an interrupt.

Sure, will fold in the following changes instead.

diff --git a/drivers/perf/arm_pmu_acpi.c b/drivers/perf/arm_pmu_acpi.c
index 845683ca7c64..d7beb035345a 100644
--- a/drivers/perf/arm_pmu_acpi.c
+++ b/drivers/perf/arm_pmu_acpi.c
@@ -98,9 +98,6 @@ 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) {
hetid = this_hetid;
@@ -111,6 +108,15 @@ arm_acpi_register_pmu_device(struct platform_device *pdev, u8 len,
}
}

+ /*
+ * This is a special case where no cpu on
+ * the system has the interrupt and which
+ * could not have been detected via above
+ * homogeneous mismatch test.
+ */
+ if (!this_gsi)
+ return 0;
+
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);