drivers: hwmon: Support for ASPEED PWM/Fan tach

The ASPEED AST2400/2500 PWM controller supports 8 PWM output ports.
The ASPEED AST2400/2500 Fan tach controller supports 16 tachometer
inputs.
The device driver matches on the device tree node. The configuration
values are read from the device tree and written to the respective
registers.
The driver provides a sysfs entries through which the user can
configure the duty-cycle value (ranging from 0 to 100 percent) and read
the fan tach rpm value.

Signed-off-by: Jaghathiswari Rankappagounder Natarajan <jaghu@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

1 files changed, 22 insertions, 0 deletions

diff --git a/Documentation/hwmon/aspeed-pwm-tacho b/Documentation/hwmon/aspeed-pwm-tacho
new file mode 100644
index 000000000000..7cfb34977460
--- /dev/null
+++ b/Documentation/hwmon/aspeed-pwm-tacho
@@ -0,0 +1,22 @@
+Kernel driver aspeed-pwm-tacho
+==============================
+
+Supported chips:
+        ASPEED AST2400/2500
+
+Authors:
+        <jaghu@google.com>
+
+Description:
+------------
+This driver implements support for ASPEED AST2400/2500 PWM and Fan Tacho
+controller. The PWM controller supports upto 8 PWM outputs. The Fan tacho
+controller supports up to 16 tachometer inputs.
+
+The driver provides the following sensor accesses in sysfs:
+
+fanX_input      ro      provide current fan rotation value in RPM as reported
+                        by the fan to the device.
+
+pwmX            rw      get or set PWM fan control value. This is an integer
+                        value between 0(off) and 255(full speed).