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

From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, suzuki.poulose@arm.com,
	yangyicong@huawei.com, Sami Mujawar <sami.mujawar@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Mike Leach <mike.leach@linaro.org>, Leo Yan <leo.yan@linaro.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	James Clark <james.clark@arm.com>,
	coresight@lists.linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V4 1/4] arm_pmu: acpi: Refactor arm_spe_acpi_register_device()
Date: Fri, 11 Aug 2023 15:55:43 +0530	[thread overview]
Message-ID: <7920ce3b-15ee-c8d8-a7c0-59009620073c@arm.com> (raw)
In-Reply-To: <20230811101201.GA6827@willie-the-truck>

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.

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