[RFC PATCH 3/8] arm: parse cpu capacity from DT

[Juri Lelli]

With the introduction of cpu capacity bindings, CPU capacities can now be
extracted from DT. Add parsing of such information at boot time. We keep
code that can produce same information, based on different DT properties
and hard-coded values, as fall-back for backward compatibility.

Cc: Russell King <linux at arm.linux.org.uk>
Signed-off-by: Juri Lelli <juri.lelli at arm.com>
---
 arch/arm/kernel/topology.c | 50 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index ec279d1..ecbff03 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -78,6 +78,35 @@ static unsigned long *__cpu_capacity;
 #define cpu_capacity(cpu)	__cpu_capacity[cpu]
 
 static unsigned long middle_capacity = 1;
+static bool capacity_from_dt = true;
+static u32 capacity_scale = SCHED_CAPACITY_SCALE;
+
+static int __init parse_cpu_capacity(struct device_node *cpu_node, int cpu)
+{
+	int ret = 1;
+	u32 cpu_capacity;
+
+	ret = of_property_read_u32(cpu_node,
+				   "capacity",
+				   &cpu_capacity);
+	if (!ret) {
+		u64 capacity;
+
+		/*
+		 * Enforce capacity <= capacity-scale.
+		 */
+		cpu_capacity = cpu_capacity <= capacity_scale ? cpu_capacity :
+			capacity_scale;
+		capacity = (cpu_capacity << SCHED_CAPACITY_SHIFT) /
+			capacity_scale;
+
+		set_capacity_scale(cpu, capacity);
+		pr_info("CPU%d: DT cpu capacity %lu\n",
+			cpu, arch_scale_cpu_capacity(NULL, cpu));
+	}
+
+	return !ret;
+}
 
 /*
  * Iterate all CPUs' descriptor in DT and compute the efficiency
@@ -99,6 +128,18 @@ static void __init parse_dt_topology(void)
 	__cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
 				 GFP_NOWAIT);
 
+	cn = of_find_node_by_path("/cpus");
+	if (!cn) {
+		pr_err("No CPU information found in DT\n");
+		return;
+	}
+
+	if (!of_property_read_u32(cn, "capacity-scale", &capacity_scale))
+		pr_info("DT cpus capacity-scale %u\n", capacity_scale);
+	else
+		pr_debug("DT cpus capacity-scale not found: assuming %u\n",
+			capacity_scale);
+
 	for_each_possible_cpu(cpu) {
 		const u32 *rate;
 		int len;
@@ -110,6 +151,13 @@ static void __init parse_dt_topology(void)
 			continue;
 		}
 
+		if (parse_cpu_capacity(cn, cpu)) {
+			of_node_put(cn);
+			continue;
+		}
+
+		capacity_from_dt = false;
+
 		for (cpu_eff = table_efficiency; cpu_eff->compatible; cpu_eff++)
 			if (of_device_is_compatible(cn, cpu_eff->compatible))
 				break;
@@ -160,7 +208,7 @@ static void __init parse_dt_topology(void)
  */
 static void update_cpu_capacity(unsigned int cpu)
 {
-	if (!cpu_capacity(cpu))
+	if (!cpu_capacity(cpu) || capacity_from_dt)
 		return;
 
 	set_capacity_scale(cpu, cpu_capacity(cpu) / middle_capacity);
-- 
2.2.2