hwmon: (aspeed-pwm-tacho) Enable both edge measurement.

The aspeed-pwm-tacho controller supports measuring the fan tach by using
leading, falling, or both edges.  This change allows the driver to
support either of the three configurations and will appropriately modify
the returned tach data.

If the controller is measuring with both edges it can return a value more
quickly to the requestor.  This version of the driver should still take ~1s
to return with an RPM value per fan, however, it can be tuned faster with
double edge counting enabled than without.

I tested this and found the number returned matched what I expected.

Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/aspeed-pwm-tacho.c

@@ -146,11 +146,20 @@
 
 #define PWM_MAX 255
 
+#define BOTH_EDGES 0x02 /* 10b */
+
 #define M_PWM_DIV_H 0x00
 #define M_PWM_DIV_L 0x05
 #define M_PWM_PERIOD 0x5F
 #define M_TACH_CLK_DIV 0x00
-#define M_TACH_MODE 0x00
+/*
+ * 5:4 Type N fan tach mode selection bit:
+ * 00: falling
+ * 01: rising
+ * 10: both
+ * 11: reserved.
+ */
+#define M_TACH_MODE 0x02 /* 10b */
 #define M_TACH_UNIT 0x1000
 #define INIT_FAN_CTRL 0xFF
 
@@ -163,6 +172,7 @@ struct aspeed_pwm_tacho_data {
 	u8 type_pwm_clock_division_h[3];
 	u8 type_pwm_clock_division_l[3];
 	u8 type_fan_tach_clock_division[3];
+	u8 type_fan_tach_mode[3];
 	u16 type_fan_tach_unit[3];
 	u8 pwm_port_type[8];
 	u8 pwm_port_fan_ctrl[8];
@@ -499,7 +509,7 @@ static int aspeed_get_fan_tach_ch_rpm(struct aspeed_pwm_tacho_data *priv,
 				      u8 fan_tach_ch)
 {
 	u32 raw_data, tach_div, clk_source, sec, val;
-	u8 fan_tach_ch_source, type;
+	u8 fan_tach_ch_source, type, mode, both;
 
 	regmap_write(priv->regmap, ASPEED_PTCR_TRIGGER, 0);
 	regmap_write(priv->regmap, ASPEED_PTCR_TRIGGER, 0x1 << fan_tach_ch);
@@ -516,7 +526,14 @@ static int aspeed_get_fan_tach_ch_rpm(struct aspeed_pwm_tacho_data *priv,
 
 	raw_data = val & RESULT_VALUE_MASK;
 	tach_div = priv->type_fan_tach_clock_division[type];
-	tach_div = 0x4 << (tach_div * 2);
+	/*
+	 * We need the mode to determine if the raw_data is double (from
+	 * counting both edges).
+	 */
+	mode = priv->type_fan_tach_mode[type];
+	both = (mode & BOTH_EDGES) ? 1 : 0;
+
+	tach_div = (0x4 << both) << (tach_div * 2);
 	clk_source = priv->clk_freq;
 
 	if (raw_data == 0)
@@ -702,6 +719,7 @@ static void aspeed_create_type(struct aspeed_pwm_tacho_data *priv)
 	aspeed_set_tacho_type_enable(priv->regmap, TYPEM, true);
 	priv->type_fan_tach_clock_division[TYPEM] = M_TACH_CLK_DIV;
 	priv->type_fan_tach_unit[TYPEM] = M_TACH_UNIT;
+	priv->type_fan_tach_mode[TYPEM] = M_TACH_MODE;
 	aspeed_set_tacho_type_values(priv->regmap, TYPEM, M_TACH_MODE,
 				     M_TACH_UNIT, M_TACH_CLK_DIV);
 }