platform/x86: thinkpad_acpi: Fix invalid fan speed on ThinkPad X120e

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

Recalculate 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@proton.me>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20250203163255.5525-1-sybdorsett@proton.me
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: Sybil Isabel Dorsett

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);