[PATCH v2] Fix invalid fan speed on ThinkPad X120e

[Sybil Isabel Dorsett]

On ThinkPad X120e, fan speed is incorrectly reported in ticks
per revolution rather than RPM.

Recaculate the fan speed value reported for ThinkPad X120e
to RPM based on a 22.5 kHz clock.

Based on the information on
https://www.thinkwiki.org/wiki/How_to_control_fan_speed,
the same problem is highly likely to be relevant to at least Edge11,
but Edge11 is not addressed in this patch.

Signed-off-by: Sybil Isabel Dorsett <sybdorsett@xxxxxxxxx>
---

Notes:
    v2: addressed review comments
        - name of the new variable is changed
          from "fan_speed_requires_conversion" to "fan_speed_in_tpr";
        - rephrased the commit message;
        - "KHz" is respelled as "kHz".

 drivers/platform/x86/thinkpad_acpi.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c
index 1fcb0f996..e7778ea41 100644
--- a/drivers/platform/x86/thinkpad_acpi.c
+++ b/drivers/platform/x86/thinkpad_acpi.c
@@ -7885,6 +7885,7 @@ static struct ibm_struct volume_driver_data = {
 
 #define FAN_NS_CTRL_STATUS	BIT(2)		/* Bit which determines control is enabled or not */
 #define FAN_NS_CTRL		BIT(4)		/* Bit which determines control is by host or EC */
+#define FAN_CLOCK_TPM		(22500*60)	/* Ticks per minute for a 22.5 kHz clock */
 
 enum {					/* Fan control constants */
 	fan_status_offset = 0x2f,	/* EC register 0x2f */
@@ -7940,6 +7941,7 @@ static int fan_watchdog_maxinterval;
 
 static bool fan_with_ns_addr;
 static bool ecfw_with_fan_dec_rpm;
+static bool fan_speed_in_tpr;
 
 static struct mutex fan_mutex;
 
@@ -8142,8 +8144,11 @@ static int fan_get_speed(unsigned int *speed)
 			     !acpi_ec_read(fan_rpm_offset + 1, &hi)))
 			return -EIO;
 
-		if (likely(speed))
+		if (likely(speed)) {
 			*speed = (hi << 8) | lo;
+			if (fan_speed_in_tpr && *speed != 0)
+				*speed = FAN_CLOCK_TPM / *speed;
+		}
 		break;
 	case TPACPI_FAN_RD_TPEC_NS:
 		if (!acpi_ec_read(fan_rpm_status_ns, &lo))
@@ -8176,8 +8181,11 @@ static int fan2_get_speed(unsigned int *speed)
 		if (rc)
 			return -EIO;
 
-		if (likely(speed))
+		if (likely(speed)) {
 			*speed = (hi << 8) | lo;
+			if (fan_speed_in_tpr && *speed != 0)
+				*speed = FAN_CLOCK_TPM / *speed;
+		}
 		break;
 
 	case TPACPI_FAN_RD_TPEC_NS:
@@ -8788,6 +8796,7 @@ static const struct attribute_group fan_driver_attr_group = {
 #define TPACPI_FAN_NOFAN	0x0008		/* no fan available */
 #define TPACPI_FAN_NS		0x0010		/* For EC with non-Standard register addresses */
 #define TPACPI_FAN_DECRPM	0x0020		/* For ECFW's with RPM in register as decimal */
+#define TPACPI_FAN_TPR		0x0040		/* Fan speed is in Ticks Per Revolution */
 
 static const struct tpacpi_quirk fan_quirk_table[] __initconst = {
 	TPACPI_QEC_IBM('1', 'Y', TPACPI_FAN_Q1),
@@ -8817,6 +8826,7 @@ static const struct tpacpi_quirk fan_quirk_table[] __initconst = {
 	TPACPI_Q_LNV3('R', '0', 'V', TPACPI_FAN_NS),	/* 11e Gen5 KL-Y */
 	TPACPI_Q_LNV3('N', '1', 'O', TPACPI_FAN_NOFAN),	/* X1 Tablet (2nd gen) */
 	TPACPI_Q_LNV3('R', '0', 'Q', TPACPI_FAN_DECRPM),/* L480 */
+	TPACPI_Q_LNV('8', 'F', TPACPI_FAN_TPR),		/* ThinkPad x120e */
 };
 
 static int __init fan_init(struct ibm_init_struct *iibm)
@@ -8887,6 +8897,8 @@ static int __init fan_init(struct ibm_init_struct *iibm)
 
 			if (quirks & TPACPI_FAN_Q1)
 				fan_quirk1_setup();
+			if (quirks & TPACPI_FAN_TPR)
+				fan_speed_in_tpr = true;
 			/* Try and probe the 2nd fan */
 			tp_features.second_fan = 1; /* needed for get_speed to work */
 			res = fan2_get_speed(&speed);
-- 
2.39.5