On Mon, Oct 27, 2014 at 09:58:10AM +0000, Hanjun Guo wrote:
[...]
> >> +static int map_gicc_mpidr(struct acpi_subtable_header *entry,
> >> + int device_declaration, u32 acpi_id, int *mpidr)
> >> +{
> >> + struct acpi_madt_generic_interrupt *gicc =
> >> + container_of(entry, struct acpi_madt_generic_interrupt, header);
> >> +
> >> + if (!(gicc->flags & ACPI_MADT_ENABLED))
> >> + return -ENODEV;
> >> +
> >> + /* In the GIC interrupt model, logical processors are
> >> + * required to have a Processor Device object in the DSDT,
> >> + * so we should check device_declaration here
> >> + */
> >> + if (device_declaration && (gicc->uid == acpi_id)) {
> >> + /*
> >> + * Only bits [0:7] Aff0, bits [8:15] Aff1, bits [16:23] Aff2
> >> + * and bits [32:39] Aff3 are meaningful, so pack the Affx
> >> + * fields into a single 32 bit identifier to accommodate the
> >> + * acpi processor drivers.
> >> + */
> >> + *mpidr = ((gicc->arm_mpidr & 0xff00000000) >> 8)
> >> + | gicc->arm_mpidr;
> >
> > The simple fact that you define a function to pack the mpidr value and
> > you can't use it here because this is *generic* code is telling, and
> > a very bad omen. At the cost of sounding like a broken record, I do not
> > like this mpidr->apic->logical_cpu song and dance at all.
> > ACPI is peppered with code (eg hotplug is another example, CPUidle driver
> > even worse) that is supposed to be generic but contains x86 code to carry
> > out this cpuid conversion, I really think that in order to start an ARM64
> > ACPI port properly we should at least try to factor out this physical to
> > logical cpu id conversion, and it is not the first time that I mention this
> > on the lists.
>
> I know, thanks for pointing this out. As I replied in previous version
> of this patch set, apic_id is x86/ia64 specific, but the meaning behind
> it is not. It means the CPU hardware id to identify itself in the system,
> it just like MPIDR on ARM.
Yes, except that it is called apic_id.
> I will send out a patch for RFC to convert apic_id to physid which
> is generic for all platforms.
That seems a good idea to sound out if I am the only one having an issue
with the current approach.
> > I will also talk to Rafael about this at the earliest opportunity, I
> > guess that x86 code relies on apic-id because some ACPI versions could
> > not rely on the acpi-id or some other reasons I have to investigate.
>
> As ACPI spec (section 8.4, Declaring Processors) said, Each processor
> in the system must be declared in the ACPI namespace, so each cpu will
> have acpi_id in all ACPI versions, and in theory we can map acpi_id to
> logical cpu id if we want to.
>
> But things are complicated, apic_id is connected to many
> tables, MADT for smp init, DSDT for device driver, and SRAT for NUMA (there
> is no acpi_id in it, ONLY has apic_id in the table for x86/ia64), so if we
> want to factor the code to map acpi_id to logical cpu id, we need to modify:
>
> - ACPI drivers;
> - SMP init for x86 and ia64
> - the mappings for NUMA init for x86 and ia64
> that will be lots of work I think.
>
> I'm willing to discuss this further and come out a solution, please
> comment on what I said and share your ideas :)
Factoring out apic_id to a common cpu_physical_id is ok to me, because
basically that's what you are doing except for the naming. I do not
have any particular preference for the acpi_id, I mentioned that only
as a means to implement a generic cpu_physical_id, arch agnostic.
Drop the RFC you mentioned above please on the list, we will restart debating
from there.
Thanks,
Lorenzo
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