Add a sysfs cpu_capacity attribute with which it is possible to read and
write (thus over-writing default values) CPUs capacity. This might be
useful in situations where values needs changing after boot.

The new attribute shows up as:

 /sys/devices/system/cpu/cpu*/cpu_capacity

Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Mark Brown <broo...@kernel.org>
Cc: Sudeep Holla <sudeep.ho...@arm.com>
Signed-off-by: Juri Lelli <juri.le...@arm.com>
---

Changes from v5:
  - add mutex to protect cpu_scale (as pointed out by Morten off-line)
---
 arch/arm64/kernel/topology.c | 73 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index b75b0ba2e113..cff34cc858b7 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -26,6 +26,7 @@
 #include <asm/topology.h>
 
 static DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
+static DEFINE_MUTEX(cpu_scale_mutex);
 
 unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
 {
@@ -37,6 +38,76 @@ static void set_capacity_scale(unsigned int cpu, unsigned 
long capacity)
        per_cpu(cpu_scale, cpu) = capacity;
 }
 
+#ifdef CONFIG_PROC_SYSCTL
+#include <asm/cpu.h>
+#include <linux/string.h>
+static ssize_t show_cpu_capacity(struct device *dev,
+                                struct device_attribute *attr,
+                                char *buf)
+{
+       struct cpu *cpu = container_of(dev, struct cpu, dev);
+       ssize_t rc;
+       int cpunum = cpu->dev.id;
+       unsigned long capacity = arch_scale_cpu_capacity(NULL, cpunum);
+
+       rc = sprintf(buf, "%lu\n", capacity);
+
+       return rc;
+}
+
+static ssize_t store_cpu_capacity(struct device *dev,
+                                 struct device_attribute *attr,
+                                 const char *buf,
+                                 size_t count)
+{
+       struct cpu *cpu = container_of(dev, struct cpu, dev);
+       int this_cpu = cpu->dev.id, i;
+       unsigned long new_capacity;
+       ssize_t ret;
+
+       if (count) {
+               char *p = (char *) buf;
+
+               ret = kstrtoul(p, 0, &new_capacity);
+               if (ret)
+                       return ret;
+               if (new_capacity > SCHED_CAPACITY_SCALE)
+                       return -EINVAL;
+
+               mutex_lock(&cpu_scale_mutex);
+               for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
+                       set_capacity_scale(i, new_capacity);
+               mutex_unlock(&cpu_scale_mutex);
+       }
+
+       return count;
+}
+
+static DEVICE_ATTR(cpu_capacity,
+                  0644,
+                  show_cpu_capacity,
+                  store_cpu_capacity);
+
+static int register_cpu_capacity_sysctl(void)
+{
+       int i;
+       struct device *cpu;
+
+       for_each_possible_cpu(i) {
+               cpu = get_cpu_device(i);
+               if (!cpu) {
+                       pr_err("%s: too early to get CPU%d device!\n",
+                              __func__, i);
+                       continue;
+               }
+               device_create_file(cpu, &dev_attr_cpu_capacity);
+       }
+
+       return 0;
+}
+late_initcall(register_cpu_capacity_sysctl);
+#endif
+
 static u32 capacity_scale;
 static u32 *raw_capacity;
 static bool cap_parsing_failed;
@@ -87,6 +158,7 @@ static void normalize_cpu_capacity(void)
                return;
 
        pr_debug("cpu_capacity: capacity_scale=%u\n", capacity_scale);
+       mutex_lock(&cpu_scale_mutex);
        for_each_possible_cpu(cpu) {
                pr_debug("cpu_capacity: cpu=%d raw_capacity=%u\n",
                         cpu, raw_capacity[cpu]);
@@ -96,6 +168,7 @@ static void normalize_cpu_capacity(void)
                pr_debug("cpu_capacity: CPU%d cpu_capacity=%lu\n",
                        cpu, arch_scale_cpu_capacity(NULL, cpu));
        }
+       mutex_unlock(&cpu_scale_mutex);
 }
 
 #ifdef CONFIG_CPU_FREQ
-- 
2.10.0

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