Re: [PATCH v3 13/17] ARM64 / ACPI: Add GICv2 specific ACPI boot support

[Tomasz Nowicki]

On 04.09.2014 12:14, Arnd Bergmann wrote:
> On Thursday 04 September 2014 12:10:28 Tomasz Nowicki wrote:
> > On 03.09.2014 20:42, Arnd Bergmann wrote:
> > > On Monday 01 September 2014 22:57:51 Hanjun Guo wrote:
> > > > +       /* Collect CPU base addresses */
> > > > +       count = acpi_parse_entries(sizeof(struct acpi_table_madt),
> > > > +                                  gic_acpi_parse_madt_cpu, table,
> > > > +                                  ACPI_MADT_TYPE_GENERIC_INTERRUPT,
> > > > +                                  ACPI_MAX_GIC_CPU_INTERFACE_ENTRIES);
> > > > +       if (count < 0) {
> > > > +               pr_err("Error during GICC entries parsing\n");
> > > > +               return -EFAULT;
> > > > +       } else if (!count) {
> > > > +               /* No GICC entries provided, use address from MADT header */
> > > > +               struct acpi_table_madt *madt = (struct acpi_table_madt *)table;
> > > > +
> > > > +               if (!madt->address)
> > > > +                       return -EFAULT;
> > > > +
> > > > +               cpu_phy_base = (u64)madt->address;
> > > > +       }
> > >
> > > After I read through ACPI-5.1 section 5.2.12.14, I wonder if this is the
> > > best way to treat a missing ACPI_MADT_TYPE_GENERIC_INTERRUPT table.
> > >
> > > Do we expect to see those in practice? It seems like using the x86 local
> > > APIC address as a fallback for the GIC address is not something we
> > > should do unless we absolutely have to support a system that doesn't
> > > have the GIC table.
> >
> > No, we do not expect and hopefully there will be no such
> >
> > But, we are trying to be as much as possible inline with 5.1 spec,
> > 5.2.12.14 says:
> > [...]
> > If provided here (CPU physical base address), the "Local Interrupt
> > Controller Address" field in the MADT must be ignored by the OSPM.
> > [...]
>
> Yes, that's what I saw. So ignoring it all the time is fine, right?
> Presumably the madt->address field is only referenced here because
> some pre-5.1 implementations used to do that.

So this is very vague statement. On the one hand it would make sense to 
take madt->address if we have no GICC entries. On the other hand we do 
not support non-banked GIC cpu registers. So all of then need to have 
the same cpu_base_address. What if one has null address? Should the rest 
take madt->address? I think you are right, I will remove madt->address 
fallback and simplify the code.

Thanks,
Tomasz
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