hwmon: (mlxreg-fan) Add support for new flavour of capability register

FAN platform data is common across the various systems, while fan
driver should be able to apply only the fan instances relevant
to specific system.

For example, platform data might contain descriptions for fan1,
fan2, ..., fan{n}, while some systems equipped with all 'n' fans,
others with less.
Also, on some systems fan drawer can be equipped with several
tachometers and on others only with one.

For detection of the real number of equipped drawers and tachometers
special capability registers are used.
These registers used to indicate presence of drawers and tachometers
through the bitmap.

For some new big modular systems this register will provide presence
data by counter.

Use slot parameter to distinct whether capability register contains
bitmask or counter.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20250113084859.27064-3-vadimp@nvidia.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: vadimp-nvidia

drivers/hwmon/mlxreg-fan.c

@@ -63,12 +63,14 @@ struct mlxreg_fan;
  * @reg: register offset;
  * @mask: fault mask;
  * @prsnt: present register offset;
+ * @shift: tacho presence bit shift;
  */
 struct mlxreg_fan_tacho {
 	bool connected;
 	u32 reg;
 	u32 mask;
 	u32 prsnt;
+	u32 shift;
 };
 
 /*
@@ -143,8 +145,10 @@ mlxreg_fan_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
 				/*
 				 * Map channel to presence bit - drawer can be equipped with
 				 * one or few FANs, while presence is indicated per drawer.
+				 * Shift channel value if necessary to align with register value.
 				 */
-				if (BIT(channel / fan->tachos_per_drwr) & regval) {
+				if (BIT(rol32(channel, tacho->shift) / fan->tachos_per_drwr) &
+					regval) {
 					/* FAN is not connected - return zero for FAN speed. */
 					*val = 0;
 					return 0;
@@ -408,7 +412,7 @@ static int mlxreg_fan_connect_verify(struct mlxreg_fan *fan,
 		return err;
 	}
 
-	return !!(regval & data->bit);
+	return data->slot ? (data->slot <= regval ? 1 : 0) : !!(regval & data->bit);
 }
 
 static int mlxreg_pwm_connect_verify(struct mlxreg_fan *fan,
@@ -545,7 +549,15 @@ static int mlxreg_fan_config(struct mlxreg_fan *fan,
 			return err;
 		}
 
-		drwr_avail = hweight32(regval);
+		/*
+		 * The number of drawers could be specified in registers by counters for newer
+		 * systems, or by bitmasks for older systems. In case the data is provided by
+		 * counter, it is indicated through 'version' field.
+		 */
+		if (pdata->version)
+			drwr_avail = regval;
+		else
+			drwr_avail = hweight32(regval);
 		if (!tacho_avail || !drwr_avail || tacho_avail < drwr_avail) {
 			dev_err(fan->dev, "Configuration is invalid: drawers num %d tachos num %d\n",
 				drwr_avail, tacho_avail);