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Subject: Re: [RFC 2/3] arm_pmu: acpi: spe: Add initial MADT/SPE probing
To:     Will Deacon <will.deacon@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-acpi@vger.kernel.org, devel@acpica.org,
        catalin.marinas@arm.com, mark.rutland@arm.com,
        robert.moore@intel.com, erik.schmauss@intel.com,
        rafael.j.wysocki@intel.com, lenb@kernel.org
References: <20190209004718.3292087-1-jeremy.linton@arm.com>
 <20190209004718.3292087-3-jeremy.linton@arm.com>
 <20190214171125.GG2475@fuggles.cambridge.arm.com>
From:   Jeremy Linton <jeremy.linton@arm.com>
Message-ID: <c740a06e-d5d3-3e42-d19b-fbfea02ac0e7@arm.com>
Date:   Thu, 14 Feb 2019 12:03:57 -0600
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Hi,

Thanks for taking a look at this..

On 2/14/19 11:11 AM, Will Deacon wrote:
> Hi Jeremy,
> 
> On Fri, Feb 08, 2019 at 06:47:17PM -0600, Jeremy Linton wrote:
>> ACPI 6.3 adds additional fields to the MADT GICC
>> structure to describe SPE PPI's. We pick these out
>> of the cached reference to the madt_gicc structure
>> similarly to the core PMU code. We then create a platform
>> device referring to the IRQ and let the user/module loader
>> decide whether to load the SPE driver.
>>
>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
>> ---
>>   arch/arm64/include/asm/acpi.h |  3 ++
>>   drivers/perf/arm_pmu_acpi.c   | 67 +++++++++++++++++++++++++++++++++++
>>   2 files changed, 70 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
>> index 2def77ec14be..f9f9f2eb5d54 100644
>> --- a/arch/arm64/include/asm/acpi.h
>> +++ b/arch/arm64/include/asm/acpi.h
>> @@ -40,6 +40,9 @@
>>   	(!(entry) || (entry)->header.length < ACPI_MADT_GICC_MIN_LENGTH || \
>>   	(unsigned long)(entry) + (entry)->header.length > (end))
>>   
>> +#define ACPI_MADT_GICC_SPE  (ACPI_OFFSET(struct acpi_madt_generic_interrupt, \
>> +	spe_overflow_interrupt) + sizeof(u16))
>> +
>>   /* Basic configuration for ACPI */
>>   #ifdef	CONFIG_ACPI
>>   pgprot_t __acpi_get_mem_attribute(phys_addr_t addr);
>> diff --git a/drivers/perf/arm_pmu_acpi.c b/drivers/perf/arm_pmu_acpi.c
>> index 0f197516d708..725d413b47dc 100644
>> --- a/drivers/perf/arm_pmu_acpi.c
>> +++ b/drivers/perf/arm_pmu_acpi.c
>> @@ -74,6 +74,71 @@ static void arm_pmu_acpi_unregister_irq(int cpu)
>>   	acpi_unregister_gsi(gsi);
>>   }
>>   
>> +static struct resource spe_resources[] = {
>> +	{
>> +		/* irq */
>> +		.flags          = IORESOURCE_IRQ,
>> +	}
>> +};
>> +
>> +static struct platform_device spe_dev = {
>> +	.name = "arm,spe-v1",
>> +	.id = -1,
>> +	.resource = spe_resources,
>> +	.num_resources = ARRAY_SIZE(spe_resources)
>> +};
>> +
>> +/*
>> + * For lack of a better place, hook the normal PMU MADT walk
>> + * and create a SPE device if we detect a recent MADT with
>> + * a homogeneous PPI mapping.
>> + */
>> +static int arm_spe_acpi_parse_irqs(void)
>> +{
>> +	int cpu, ret, irq;
>> +	u16 gsi = 0;
>> +	bool first = true;
>> +
>> +	struct acpi_madt_generic_interrupt *gicc;
>> +
>> +	/*
>> +	 * sanity check all the GICC tables for the same interrupt number
>> +	 * for now we only support homogeneous ACPI/SPE machines.
>> +	 */
>> +	for_each_possible_cpu(cpu) {
>> +		gicc = acpi_cpu_get_madt_gicc(cpu);
>> +
>> +		if (gicc->header.length < ACPI_MADT_GICC_SPE)
>> +			return -ENODEV;
>> +
>> +		if (first) {
>> +			gsi = gicc->spe_overflow_interrupt;
>> +			if (!gsi)
>> +				return -ENODEV;
>> +			first = false;
>> +		} else if (gsi != gicc->spe_overflow_interrupt) {
>> +			pr_warn("ACPI: SPE must have homogeneous interrupts\n");
>> +			return -EINVAL;
>> +		}
> 
> Unfortunately, I don't think this is sufficient to detect a homogeneous
> system: we'll have to check the MIDRs instead, which is nasty. I would
> personally be in favour of enforcing homogeneity for ACPI systems when we
> bring up secondary CPUs, but I suspect others would disagree.

Given that all the SPE capable machines i'm aware of at the moment are 
homogeneous, are we ok with just doing an online CPU MIDR check for now, 
and cleaning that up if/when someone builds a machine and complains?

Thanks,