Re: [PATCH V3 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,
	Sami Mujawar <sami.mujawar@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Mike Leach <mike.leach@linaro.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	coresight@lists.linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V3 1/4] arm_pmu: acpi: Refactor arm_spe_acpi_register_device()
Date: Wed, 9 Aug 2023 12:31:56 +0530	[thread overview]
Message-ID: <a6b50669-37f2-98dd-e137-c76add8edbc0@arm.com> (raw)
In-Reply-To: <20230808132157.GB2369@willie-the-truck>

On 8/8/23 18:51, Will Deacon wrote:
> On Mon, Aug 07, 2023 at 11:03:40AM +0530, Anshuman Khandual wrote:
>> On 8/4/23 22:09, Will Deacon wrote:
>>> On Thu, Aug 03, 2023 at 11:43:27AM +0530, Anshuman Khandual wrote:
>>>> On 8/3/23 11:26, 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;
>>>>
>>>> Moved parse_gsi() return code checking to its original place just to
>>>> make it similar in semantics to existing 'gicc->header.length check'.
>>>> If 'gsi' is valid i.e atleast a single cpu has been probed, return
>>>> -ENXIO indicating mismatch, otherwise just return 0.
>>>
>>> Wouldn't that still be the case without the check in this hunk? We'd run
>>> into the homogeneous check and return -ENXIO from there, no?
>> Although the return code will be the same i.e -ENXIO, but not for the same reason.
>>
>> 		this_gsi = parse_gsi(gicc);
>> 		if (!this_gsi)
>> 			return gsi ? -ENXIO : 0;
>>
>> This returns 0 when IRQ could not be parsed for the first cpu, but returns -ENXIO
>> for subsequent cpus. Although return code -ENXIO here still indicates IRQ parsing
>> to have failed.
>>
>> 		} else if (hetid != this_hetid || gsi != this_gsi) {
>> 			pr_warn("ACPI: %s: must be homogeneous\n", pdev->name);
>> 			return -ENXIO;
>> 		} 
>>
>> This returns -ENXIO when there is a IRQ mismatch. But if the above check is not
>> there, -ENXIO return code here could not be classified into IRQ parse problem or
>> mismatch without looking into the IRQ value.
> 
> Sorry, but I don't understand your point here. If any of this fails, there's
> going to be some debugging needed to look at the ACPI tables; the only
> difference with my suggestion is that you'll get a message indicating that
> the devices aren't homogeneous, which I think is helpful.

I dont have strong opinion either way. Hence will move 'this_gsi' check inside the
!gsi conditional check like you had suggested earlier.

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