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

Jon Masters jcm at redhat.com
Tue Sep 9 09:04:15 PDT 2014

On 09/09/2014 12:00 PM, Hanjun Guo wrote:
> On 2014年09月09日 13:44, Jon Masters wrote:
>> 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...
> No, you didn't miss it, I'm still working on the new version, sorry I didn't
> clarify that in my previous email.

Thanks. If you could copy me on the next posting that would rock. In a
few hours we should have another platform posted as an example. In
addition, a couple of lower priority patches (building upon the core
ACPI pieces) should be posted as well.


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