This patch adds support for fan control on T2 Macs in the applesmc driver.
It introduces functions to handle floating-point fan speed values 
(which are required by t2 chips).
The fan speed reading and writing are updated
to support both integer and floating-point values.
The fan manual control is also updated to handle T2 Mac-specific keys.

Guenter Roeck asked "Does this limit still apply?"
so yes the limit still applies.

Changes since v3:
--- fixed error by kernel test robot about FIELD_GET and FIELD_PREP by
	by adding linux/bitfield.h

Co-developed-by: Aun-Ali Zaidi <admin@kodeit.net>
Signed-off-by: Aun-Ali Zaidi <admin@kodeit.net>

Signed-off-by: Atharva Tiwari <evepolonium@gmail.com>
---
 drivers/hwmon/applesmc.c | 123 ++++++++++++++++++++++++++++++++-------
 1 file changed, 101 insertions(+), 22 deletions(-)

diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index fc6d6a9053ce..f899b17dcc1e 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -33,6 +33,7 @@
 #include <linux/workqueue.h>
 #include <linux/err.h>
 #include <linux/bits.h>
+#include <linux/bitfield.h>
 
 /* data port used by Apple SMC */
 #define APPLESMC_DATA_PORT	0x300
@@ -74,6 +75,7 @@
 #define FAN_ID_FMT		"F%dID" /* r-o char[16] */
 
 #define TEMP_SENSOR_TYPE	"sp78"
+#define FAN_MANUAL_FMT		"F%dMd"
 
 /* List of keys used to read/write fan speeds */
 static const char *const fan_speed_fmt[] = {
@@ -511,6 +513,32 @@ static int applesmc_read_s16(const char *key, s16 *value)
 	return 0;
 }
 
+static inline u32 applesmc_float_to_u32(u32 d)
+{
+	u8 sign = FIELD_GET(BIT(31), d);
+	s32 exp = FIELD_GET(BIT_MASK(8) << 23, d) - 0x7F;
+	u32 fr = d & ((1u << 23) - 1);
+
+	if (sign || exp < 0)
+		return 0;
+
+	return BIT(exp) + (fr >> (23 - exp));
+}
+
+static inline u32 applesmc_u32_to_float(u32 d)
+{
+	u32 dc = d, bc = 0, exp;
+
+	if (!d)
+		return 0;
+	while (dc >>= 1)
+		++bc;
+	exp = 0x7F + bc;
+	return FIELD_PREP(BIT_MASK(8) << 23, exp) |
+			(d << (23 - (exp - 0x7F)) & BIT_MASK(23));
+
+}
+
 /*
  * applesmc_device_init - initialize the accelerometer.  Can sleep.
  */
@@ -841,16 +869,33 @@ static ssize_t applesmc_show_fan_speed(struct device *dev,
 	int ret;
 	unsigned int speed = 0;
 	char newkey[5];
-	u8 buffer[2];
+	u8 buffer[4] = {0};
+	const struct applesmc_entry *entry;
+	bool is_float = false;
 
 	scnprintf(newkey, sizeof(newkey), fan_speed_fmt[to_option(attr)],
 		  to_index(attr));
 
-	ret = applesmc_read_key(newkey, buffer, 2);
+	entry = applesmc_get_entry_by_key(newkey);
+	if (IS_ERR(entry))
+		return PTR_ERR(entry);
+
+	if (!strcmp(entry->type, "flt"))
+		is_float = true;
+
+	if (is_float) {
+		ret = applesmc_read_entry(entry, buffer, 4);
+		if (ret)
+			return ret;
+		speed = applesmc_float_to_u32(*(u32 *)buffer);
+	} else {
+		ret = applesmc_read_entry(entry, buffer, 2);
+		if (ret)
+			return ret;
+		speed = ((buffer[0] << 8 | buffer[1]) >> 2);
+	}
 	if (ret)
 		return ret;
-
-	speed = ((buffer[0] << 8 | buffer[1]) >> 2);
 	return sysfs_emit(sysfsbuf, "%u\n", speed);
 }
 
@@ -861,7 +906,9 @@ static ssize_t applesmc_store_fan_speed(struct device *dev,
 	int ret;
 	unsigned long speed;
 	char newkey[5];
-	u8 buffer[2];
+	u8 buffer[4];
+	const struct applesmc_entry *entry;
+	bool is_float = false;
 
 	if (kstrtoul(sysfsbuf, 10, &speed) < 0 || speed >= 0x4000)
 		return -EINVAL;		/* Bigger than a 14-bit value */
@@ -869,9 +916,20 @@ static ssize_t applesmc_store_fan_speed(struct device *dev,
 	scnprintf(newkey, sizeof(newkey), fan_speed_fmt[to_option(attr)],
 		  to_index(attr));
 
-	buffer[0] = (speed >> 6) & 0xff;
-	buffer[1] = (speed << 2) & 0xff;
-	ret = applesmc_write_key(newkey, buffer, 2);
+	entry = applesmc_get_entry_by_key(newkey);
+	if (IS_ERR(entry))
+		return PTR_ERR(entry);
+	if (!strcmp(entry->type, "flt"))
+		is_float = true;
+
+	if (is_float) {
+		*(u32 *)buffer = applesmc_u32_to_float(speed);
+		ret = applesmc_write_entry(entry, buffer, 4);
+	} else {
+		buffer[0] = (speed >> 6) & 0xff;
+		buffer[1] = (speed << 2) & 0xff;
+		ret = applesmc_write_entry((const struct applesmc_entry *)newkey, buffer, 2);
+	}
 
 	if (ret)
 		return ret;
@@ -885,12 +943,23 @@ static ssize_t applesmc_show_fan_manual(struct device *dev,
 	int ret;
 	u16 manual = 0;
 	u8 buffer[2];
+	char newkey[5];
+	bool has_newkey = false;
+
+	scnprintf(newkey, sizeof(newkey), FAN_MANUAL_FMT, to_index(attr));
+
+	ret = applesmc_has_key(newkey, &has_newkey);
+	if (has_newkey) {
+		ret = applesmc_read_key(newkey, buffer, 1);
+		manual = buffer[0] & 0x01;
+	} else {
+		ret = applesmc_read_key(FANS_MANUAL, buffer, 2);
+		manual = ((buffer[0] << 8 | buffer[1]) >> to_index(attr)) & 0x01;
+	}
 
-	ret = applesmc_read_key(FANS_MANUAL, buffer, 2);
 	if (ret)
 		return ret;
 
-	manual = ((buffer[0] << 8 | buffer[1]) >> to_index(attr)) & 0x01;
 	return sysfs_emit(sysfsbuf, "%d\n", manual);
 }
 
@@ -900,28 +969,38 @@ static ssize_t applesmc_store_fan_manual(struct device *dev,
 {
 	int ret;
 	u8 buffer[2];
+	char newkey[5];
+	bool has_newkey = false;
 	unsigned long input;
 	u16 val;
 
 	if (kstrtoul(sysfsbuf, 10, &input) < 0)
 		return -EINVAL;
 
-	ret = applesmc_read_key(FANS_MANUAL, buffer, 2);
-	if (ret)
-		goto out;
-
-	val = (buffer[0] << 8 | buffer[1]);
+	scnprintf(newkey, sizeof(newkey), FAN_MANUAL_FMT, to_index(attr));
 
-	if (input)
-		val = val | (0x01 << to_index(attr));
-	else
-		val = val & ~(0x01 << to_index(attr));
+	ret = applesmc_has_key(newkey, &has_newkey);
+	if (ret)
+		return ret;
+	if (has_newkey) {
+		buffer[0] = (input != 0x00);
+		ret = applesmc_write_key(newkey, buffer, 1);
+	} else {
+		ret = applesmc_read_key(FANS_MANUAL, buffer, 2);
+		val = (buffer[0] << 8 | buffer[1]);
+		if (ret)
+			goto out;
 
-	buffer[0] = (val >> 8) & 0xFF;
-	buffer[1] = val & 0xFF;
+		if (input)
+			val = val | (0x01 << to_index(attr));
+		else
+			val = val & ~(0x01 << to_index(attr));
 
-	ret = applesmc_write_key(FANS_MANUAL, buffer, 2);
+		buffer[0] = (val >> 8) & 0xFF;
+		buffer[1] = val & 0xFF;
 
+		ret = applesmc_write_key(FANS_MANUAL, buffer, 2);
+	}
 out:
 	if (ret)
 		return ret;
-- 
2.39.5