linux-kernel - Re: [PATCH V3 1/4] arm_pmu: acpi: Refactor arm_spe_acpi_register

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Date:   Tue, 8 Aug 2023 14:21:57 +0100
From:   Will Deacon <will@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com,
        Sami Mujawar <sami.mujawar@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/4] arm_pmu: acpi: Refactor
 arm_spe_acpi_register_device()

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.

Will