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hwmon: (aspeed-pwm-tacho) reduce fan_tach period 

Reduce the fan_tach period such that the fan controller uses a shorter
period to measure the rpm.

The original period of 0x1000 was chosen as a conversative value from the
reference implementation.  Through experimentation on the quanta-q71l
board, I was able to drive the number down which ultimately reduced the
time the controller would use to determine the fan_tach.  This value was
recently tested and accepted downstream on the IBM Zaius board which uses
the ast2500.

Future work: It may be worthwhile as this is a tunable parameter to the
system, to allow overriding it through the device tree.

Testing: Tested on an ast2400 sitting on a quanta-q71l and ast2500 on
power9.

Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Patrick Venture 2017-06-24 08:39:32 -07:00 committed by Guenter Roeck
parent 3a2b3d37e1
commit ece0c03a9e
1 changed files with 1 additions and 1 deletions
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2
drivers/hwmon/aspeed-pwm-tacho.c
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@ -160,7 +160,7 @@
* 11: reserved.
*/
#define M_TACH_MODE 0x02 /* 10b */
#define M_TACH_UNIT 0x1000
#define M_TACH_UNIT 0x00c0
#define INIT_FAN_CTRL 0xFF
struct aspeed_pwm_tacho_data {