linux-kernel - Re: [PATCH V4 1/4] arm_pmu: acpi: Refactor arm_spe_acpi_register

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Message-ID: <c2448e06-b46f-8a6d-163d-32364954fc23@arm.com>
Date:   Wed, 9 Aug 2023 13:54:55 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Will Deacon <will@...nel.org>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org, yangyicong@...wei.com,
        Sami Mujawar <sami.mujawar@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        James Clark <james.clark@....com>, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 1/4] arm_pmu: acpi: Refactor
 arm_spe_acpi_register_device()

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@....com>
>>> Cc: Will Deacon <will@...nel.org>
>>> Cc: Mark Rutland <mark.rutland@....com>
>>> Cc: linux-arm-kernel@...ts.infradead.org
>>> Cc: linux-kernel@...r.kernel.org
>>> Co-developed-by: Will Deacon <will@...nel.org>
>>> Signed-off-by: Will Deacon <will@...nel.org>
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....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