[PATCH v3 09/17] ARM64 / ACPI: Parse MADT for SMP initialization

Jon Masters jcm at redhat.com
Mon Sep 8 22:44:00 PDT 2014

On 09/09/2014 12:57 AM, Hanjun Guo wrote:
> Hi Jon,
> On 2014年09月09日 12:23, Jon Masters wrote:
>> On 09/01/2014 10:57 AM, Hanjun Guo wrote:
>>> MADT contains the information for MPIDR which is essential for
>>> SMP initialization, parse the GIC cpu interface structures to
>>> get the MPIDR value and map it to cpu_logical_map(), and add
>>> enabled cpu with valid MPIDR into cpu_possible_map.
>>> ACPI 5.1 only has two explicit methods to boot up SMP, PSCI and
>>> Parking protocol, but the Parking protocol is only specified for
>>> ARMv7 now, so make PSCI as the only way for the SMP boot protocol
>>> before some updates for the ACPI spec or the Parking protocol spec.
>>> +	/* CPU 0 was already initialized */
>>> +	if (cpu) {
>>> +		if (cpu_ops[cpu]->cpu_init(NULL, cpu))
>>> +			return -EOPNOTSUPP;
>>> +
>>> +		/* map the logical cpu id to cpu MPIDR */
>>> +		cpu_logical_map(cpu) = mpidr;
>> I'm not sure it's worth noting in a comment or just in the dialogue that
>> none of these MPIDR values is literally the value in the MPIDR. Linux
>> doesn't store that anyway (even in the cpu_logical_map), since it is
>> pre-filtered against MPIDR_HWID_BITMASK to remove the non-affinity level
>> bits. And since the ACPI5.1 specification requires that non-affinity
>> bits be zero everything works. But it relies upon this assumption so it
>> might be worth explicitly masking out the bits when making the call into:
>>        acpi_map_gic_cpu_interface(processor->arm_mpidr,
>>                processor->flags & ACPI_MADT_ENABLED);
>> During the parsing of the processor object's MPIDR value.
> Yes, I agree with you. When I tested this patch set on our
> ARM64 platform, I found this problem too. some firmware
> will just present the real MPIDR value to OS which some reserved
> bit set to 1, and it will lead to some logic problem in this patch.
> (actually firmware didn't obey with ACPI spec)
> I had updated the patch with:
> +	acpi_map_gic_cpu_interface(processor->arm_mpidr & MPIDR_HWID_BITMASK,
> +		processor->flags & ACPI_MADT_ENABLED);
> and then the problem was gone :)

Did I miss an updated patch posting then? It is possible...I was keeping
out of this thread for "obvious" reasons (I'm somewhat biased in favor
of ACPI on 64-bit ARM server platforms and thus not objective in all
cases...so I am confining my feedback to technical specifics). But it's
necessary that there be a little more discussion here. I've got a couple
of requests into various vendors to get more vocal too.


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