On 2013?12?04? 23:47, Rob Herring wrote:

On Tue, Dec 3, 2013 at 10:39 AM, Hanjun Guo [off-list ref] wrote:

quoted

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 <redacted>
---
  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]

quoted

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?

quoted

                 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]

quoted

@@ -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.

quoted

+
+/*
+ * 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