[RFC] ARC: setup cpu possible mask according to status field in dts

[Eugeniy Paltsev]

As we have option in u-boot to set CPU mask for running linux,
we want to pass information to kernel about CPU cores should
be brought up.

So we patch kernel dtb in u-boot to set CPUs status.

On linux boot we setup cpu possible mask according to status
field in each cpu node. It is generic method according to ePAPR:
  status - a standard property describing the state of a CPU.
  This property shall be present for nodes representing CPUs in a
  symmetric multiprocessing (SMP) configuration. For a CPU node
  the meaning of the "okay" and "disabled" values are as follows:
  "okay" - The CPU is running; "disabled" - The CPU is in a
  quiescent state."

Also we setup MCIP debug mask according cpu possible mask.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
---
 arch/arc/kernel/mcip.c | 10 ++++++++--
 arch/arc/kernel/smp.c  | 30 ++++++++++++++++++++++++++----
 2 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
index f61a52b..246481d 100644
--- a/arch/arc/kernel/mcip.c
+++ b/arch/arc/kernel/mcip.c
@@ -89,6 +89,8 @@ static void mcip_ipi_clear(int irq)
 static void mcip_probe_n_setup(void)
 {
 	struct mcip_bcr mp;
+	u32 mcip_mask = 0;
+	int i;
 
 	READ_BCR(ARC_REG_MCIP_BCR, mp);
 
@@ -102,9 +104,13 @@ static void mcip_probe_n_setup(void)
 
 	cpuinfo_arc700[0].extn.gfrc = mp.gfrc;
 
+	for (i = 0; i < NR_CPUS; i++)
+		if (cpu_possible(i))
+			mcip_mask |= BIT(i);
+
 	if (mp.dbg) {
-		__mcip_cmd_data(CMD_DEBUG_SET_SELECT, 0, 0xf);
-		__mcip_cmd_data(CMD_DEBUG_SET_MASK, 0xf, 0xf);
+		__mcip_cmd_data(CMD_DEBUG_SET_SELECT, 0, mcip_mask);
+		__mcip_cmd_data(CMD_DEBUG_SET_MASK, 0xf, mcip_mask);
 	}
 }
 
diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
index efe8b42..ee8b20a 100644
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -24,6 +24,8 @@
 #include <linux/reboot.h>
 #include <linux/irqdomain.h>
 #include <linux/export.h>
+#include <linux/of_fdt.h>
+#include <linux/libfdt.h>
 
 #include <asm/processor.h>
 #include <asm/setup.h>
@@ -47,6 +49,29 @@ void __init smp_prepare_boot_cpu(void)
 {
 }
 
+/* Mark cpu as possible if cpu status is "okay" or status absents */
+void __init smp_init_cpumask(void)
+{
+	const struct fdt_property *prop;
+	char fdt_cpu_path[25];
+	unsigned int i, oft;
+
+	for (i = 0; i < NR_CPUS; i++) {
+		sprintf(fdt_cpu_path, "/cpus/cpu@%u", i);
+		oft = fdt_path_offset(initial_boot_params, fdt_cpu_path);
+		prop = fdt_get_property(initial_boot_params, oft, "status", NULL);
+
+		/* No status property == status OK */
+		if (!prop) {
+			set_cpu_possible(i, true);
+			continue;
+		}
+
+		if (!strcmp("okay", prop->data))
+			set_cpu_possible(i, true);
+	}
+}
+
 /*
  * Called from setup_arch() before calling setup_processor()
  *
@@ -58,10 +83,7 @@ void __init smp_prepare_boot_cpu(void)
  */
 void __init smp_init_cpus(void)
 {
-	unsigned int i;
-
-	for (i = 0; i < NR_CPUS; i++)
-		set_cpu_possible(i, true);
+	smp_init_cpumask();
 
 	if (plat_smp_ops.init_early_smp)
 		plat_smp_ops.init_early_smp();
-- 
2.9.3