[PATCH] ARC: [SMP] get CPUs mask from DT

[Noam Camus]

From: Noam Camus <noamca at mellanox.com>

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