ACPI: ibm-acpi: fix and extend fan enable

This patch fix fan enable to attempt to do the right thing and not slow
down the fan if it is forced to the maximum speed.  It also extends fan
enable to work on older thinkpads.

ABI changes:
	1.  Support enable/disable for all level-based write access modes
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>

drivers/acpi/ibm_acpi.c

@@ -1820,7 +1820,8 @@ static int fan_init(void)
 	if (sfan_handle) {
 		/* 570, 770x-JL */
 		fan_control_access_mode = IBMACPI_FAN_WR_ACPI_SFAN;
-		fan_control_commands |= IBMACPI_FAN_CMD_LEVEL;
+		fan_control_commands |=
+		    IBMACPI_FAN_CMD_LEVEL | IBMACPI_FAN_CMD_ENABLE;
 	} else {
 		if (!gfan_handle) {
 			/* gfan without sfan means no fan control */
@@ -1980,10 +1981,34 @@ static int fan_set_level(int level)
 
 static int fan_set_enable(void)
 {
+	u8 s;
+	int rc;
+
 	switch (fan_control_access_mode) {
 	case IBMACPI_FAN_WR_ACPI_FANS:
 	case IBMACPI_FAN_WR_TPEC:
-		if (!acpi_ec_write(fan_status_offset, 0x80))
+		if ((rc = fan_get_status(&s)) < 0)
+			return rc;
+
+		/* Don't go out of emergency fan mode */
+		if (s != 7)
+			s = IBMACPI_FAN_EC_AUTO;
+
+		if (!acpi_ec_write(fan_status_offset, s))
+			return -EIO;
+		break;
+
+	case IBMACPI_FAN_WR_ACPI_SFAN:
+		if ((rc = fan_get_status(&s)) < 0)
+			return rc;
+
+		s &= 0x07;
+
+		/* Set fan to at least level 4 */
+		if (s < 4)
+			s = 4;
+
+		if (!acpi_evalf(sfan_handle, NULL, NULL, "vd", s))
 			return -EIO;
 		break;
 
@@ -2002,6 +2027,11 @@ static int fan_set_disable(void)
 			return -EIO;
 		break;
 
+	case IBMACPI_FAN_WR_ACPI_SFAN:
+		if (!acpi_evalf(sfan_handle, NULL, NULL, "vd", 0x00))
+			return -EIO;
+		break;
+
 	default:
 		return -ENXIO;
 	}