Re: [RFC part2 PATCH 2/9] ARM64 / ACPI: Prefill cpu possible/presentmaps and map logical cpu id to APIC id

[Hanjun Guo]

On 2013å12æ04æ 23:47, Rob Herring wrote:
> On Tue, Dec 3, 2013 at 10:39 AM, Hanjun Guo <hanjun.guo@xxxxxxxxxx> wrote:
> > When boot the kernel with MADT, the cpu possible and present maps should be
> > prefilled for cpu topology and acpi based cpu hot-plug.
> >
> > The logic cpu id maps to APIC id (GIC id) is also implemented, it is needed
> > for acpi processor drivers.
> >
> > Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
> > ---
> >   arch/arm64/include/asm/acpi.h |   10 ++--
> >   arch/arm64/kernel/setup.c     |    2 +
> >   arch/arm64/kernel/smp.c       |    2 +
> >   drivers/acpi/plat/arm-core.c  |  118 +++++++++++++++++++++++++++++++++++++++++
> >   4 files changed, 129 insertions(+), 3 deletions(-)
> [snip]
>
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index a0c2ca6..1428024 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -420,7 +420,9 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
> >                  if (err)
> >                          continue;
> >
> > +#ifndef CONFIG_ACPI
> >                  set_cpu_present(cpu, true);
> > +#endif
> Should this be moved to DT cpu topology related code?

I didn't see the code in the mainline, Mark Brown is
working on it now?

> >                  max_cpus--;
> >          }
> >   }
> > diff --git a/drivers/acpi/plat/arm-core.c b/drivers/acpi/plat/arm-core.c
> > index 45ff625..8527ecc 100644
> > --- a/drivers/acpi/plat/arm-core.c
> > +++ b/drivers/acpi/plat/arm-core.c
> [snip]
>
> > @@ -221,6 +284,61 @@ static int __init acpi_parse_madt_gic_distributor_entries(void)
> >          return 0;
> >   }
> >
> > +static int setup_possible_cpus __initdata = -1;
> > +static int __init _setup_possible_cpus(char *str)
> > +{
> > +       get_option(&str, &setup_possible_cpus);
> > +       return 0;
> > +}
> > +early_param("possible_cpus", _setup_possible_cpus);
> This does not seem ACPI or ARM specific.
>
> > +
> > +/*
> > + * cpu_possible_mask should be static, it cannot change as cpu's
> > + * are onlined, or offlined. The reason is per-cpu data-structures
> > + * are allocated by some modules at init time, and dont expect to
> > + * do this dynamically on cpu arrival/departure.
> > + * cpu_present_mask on the other hand can change dynamically.
> > + * In case when cpu_hotplug is not compiled, then we resort to current
> > + * behaviour, which is cpu_possible == cpu_present.
> > + * - Ashok Raj
> > + *
> > + * Three ways to find out the number of additional hotplug CPUs:
> > + * - If the BIOS specified disabled CPUs in ACPI/mptables use that.
> > + * - The user can overwrite it with possible_cpus=NUM
> > + * - Otherwise don't reserve additional CPUs.
> > + * We do this because additional CPUs waste a lot of memory.
> > + * -AK
> > + */
> > +void __init prefill_possible_map(void)
> > +{
> > +       int i;
> > +       int possible, disabled_cpus;
> > +
> > +       disabled_cpus = total_cpus - available_cpus;
> > +
> > +       if (setup_possible_cpus == -1) {
> > +               if (disabled_cpus > 0)
> > +                       setup_possible_cpus = disabled_cpus;
> > +               else
> > +                       setup_possible_cpus = 0;
> > +       }
> > +
> > +       possible = available_cpus + setup_possible_cpus;
> > +
> > +       pr_info("SMP: the system is limited to %d CPUs\n", nr_cpu_ids);
> > +
> > +       if (possible > nr_cpu_ids)
> > +               possible = nr_cpu_ids;
> > +
> > +       pr_info("SMP: Allowing %d CPUs, %d hotplug CPUs\n",
> > +               possible, max((possible - available_cpus), 0));
> > +
> > +       for (i = 0; i < possible; i++)
> > +               set_cpu_possible(i, true);
> > +       for (; i < NR_CPUS; i++)
> > +               set_cpu_possible(i, false);
> > +}
> This does not seem ACPI or ARM specific either.

I think possible map here is related to ACPI based CPU hot-plug,
that's why I introduce the code here, if anything I'm wrong, please
correct me.

Thanks
Hanjun
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