From: Noam Camus <noamca@xxxxxxxxxxxx>
Today we use smp_init_cpus() to set cpu possible mask
and we use smp_prepare_cpus() to set cpu present mask.
For possible mask we use all CPUs at range [0-NR_CPUS] and
for present mask we use all CPUs at range [0-max_cpus]
which is actually the same as possible mask (no hutplug).
For platform like eznps we wish to have more configurable range then
being statically defined by NR_CPUS (actuall derived from CONFIG_NR_CPUS).
For this purpose we added two new entries at our device tree root level:
possible-cpus
present-cpus
The format of this new entries is same like for all similar kernel
parameters which provide cpu list (see Documentation/kernel-parameters.txt)
example of use would be (assume CONFIG_NR_CPUS=8):
present-cpus = "0-1,6-7";
possible-cpus = "0-7";
Now if we provide such list in our DT then we won't use the statically range.
In our example above only CPUs 0,1,6,7 will be up after boot.
Signed-off-by: Noam Camus <noamca at mellanox.com>
---
arch/arc/kernel/smp.c | 32 ++++++++++++++++++++++++++++----
1 files changed, 28 insertions(+), 4 deletions(-)
diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
index 03d5151..5855403 100644
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -16,6 +16,7 @@
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/profile.h>
+#include <linux/of_fdt.h>
#include <linux/mm.h>
#include <linux/cpu.h>
#include <linux/irq.h>
@@ -34,6 +35,21 @@ arch_spinlock_t smp_bitops_lock = __ARCH_SPIN_LOCK_UNLOCKED;
struct plat_smp_ops __weak plat_smp_ops;
+/* Get CPUs mask from device tree */
+static int __init smp_get_cpumask(const char *name, struct cpumask *cpumask)
+{
+ unsigned long dt_root = of_get_flat_dt_root();
+ const char *buf;
+
+ buf = of_get_flat_dt_prop(dt_root, name, NULL);
+ if (!buf)
+ return 0;
+
+ cpulist_parse(buf, cpumask);
+
+ return 1;
+}
+
/* XXX: per cpu ? Only needed once in early seconday boot */
struct task_struct *secondary_idle_tsk;
@@ -54,9 +70,13 @@ void __init smp_prepare_boot_cpu(void)
void __init smp_init_cpus(void)
{
unsigned int i;
+ struct cpumask cpumask;
- for (i = 0; i < NR_CPUS; i++)
- set_cpu_possible(i, true);
+ if (smp_get_cpumask("possible-cpus", &cpumask))
+ init_cpu_possible(&cpumask);
+ else
+ for (i = 0; i < NR_CPUS; i++)
+ set_cpu_possible(i, true);
if (plat_smp_ops.init_early_smp)
plat_smp_ops.init_early_smp();
@@ -66,13 +86,17 @@ void __init smp_init_cpus(void)
void __init smp_prepare_cpus(unsigned int max_cpus)
{
int i;
+ struct cpumask cpumask;
/*
* Initialise the present map, which describes the set of CPUs
* actually populated at the present time.
*/
- for (i = 0; i < max_cpus; i++)
- set_cpu_present(i, true);
+ if (smp_get_cpumask("present-cpus", &cpumask))
+ init_cpu_present(&cpumask);
+ else
+ for (i = 0; i < max_cpus; i++)
+ set_cpu_present(i, true);
}
void __init smp_cpus_done(unsigned int max_cpus)
--
1.7.1
