cpufreq/arm-bl-cpufreq: Add simple cpufreq big.LITTLE switcher frontend

This patch adds a very simple cpufreq-based frontend to the ARM
big.LITTLE switcher.

This driver simply simulates two performance points corresponding
to the big and little clusters.

There is currently no interface for reporting what the dummy
frequencies exposed by the driver actually mean in terms of real
cluster / performance point combinations.  For the very simple case
supported, cpuinfo_max_freq corresponds to big and cpuinfo_min_freq
corresponds to LITTLE.

Signed-off-by: Dave Martin <dave.martin@linaro.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/Documentation/cpu-freq/cpufreq-arm-bl.txt b/Documentation/cpu-freq/cpufreq-arm-bl.txt
new file mode 100644
index 00000000000..52e2f3ad761
--- /dev/null
+++ b/Documentation/cpu-freq/cpufreq-arm-bl.txt
@@ -0,0 +1,47 @@
+Synchronous cluster switching interface for the ARM big.LITTLE switcher
+-----------------------------------------------------------------------
+
+The arm-bl-cpufreq driver provides a simple interface which models two
+clusters as two performance points.
+
+Within each CPU's cpufreq directory in sysfs
+(/sys/devices/system/cpu/cpu?/cpufreq/):
+
+cpuinfo_max_freq:
+
+	reports the dummy frequency value which corresponds to the "big"
+	cluster.
+
+cpuinfo_min_freq:
+
+	reports the dummy frequency value which corresponds to the
+	"little" cluster.
+
+cpuinfo_cur_freq:
+
+	reports the dummy frequency corresponding to the currently
+	running cluster.
+
+
+To switch clusters, either the built-in "powersave" or "performance"
+governors can be used to force the "little" or "big" cluster
+respectively; or alternatively the "userspace" governor can be used,
+
+The following script fragment demonstrates how the userspace governor
+can be used to switch:
+
+
+for x in /sys/devices/system/cpu/cpu[0-9]*; do
+	echo userspace >$x/cpufreq/scaling_governor
+done
+
+big_freq=`cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq`
+little_freq=`cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq`
+
+switch_to_big () {
+	echo $big_freq >/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
+}
+
+switch_to_little () {
+	echo $little_freq >/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
+}