[PATCH 10/21] ACPI: ibm-acpi: document fan control

Henrique de Moraes Holschuh
2006-11-25T20:45:17Z

This patch documents the ThinkPad fan control strategies. Source of the
data:

0. ibm-acpi source
1. DSDTs for various ThinkPads (770, X31, X40, X41, T43, A21m, T22)
2. http://thinkwiki.org/wiki/Embedded_Controller_Firmware#Firmware_Issues
3. http://thinkwiki.org/wiki/How_to_control_fan_speed
4. Various threads about windows fan control utilities in thinkpads.com

Signed-off-by: Henrique de Moraes Holschuh <hmh-N3TV7GIv+o9fyO9Q7EP/yw@public.gmane.org>
---

drivers/acpi/ibm_acpi.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 108 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/ibm_acpi.c b/drivers/acpi/ibm_acpi.c
index 5258994..ccbb17c 100644
--- a/drivers/acpi/ibm_acpi.c
+++ b/drivers/acpi/ibm_acpi.c
@@ -205,7 +205,7 @@ IBM_HANDLE(led, ec, "SLED", /* 570 */
IBM_HANDLE(beep, ec, "BEEP"); /* all except R30, R31 */
IBM_HANDLE(ecrd, ec, "ECRD"); /* 570 */
IBM_HANDLE(ecwr, ec, "ECWR"); /* 570 */
-IBM_HANDLE(fans, ec, "FANS"); /* X31, X40 */
+IBM_HANDLE(fans, ec, "FANS"); /* X31, X40, X41 */

IBM_HANDLE(gfan, ec, "GFAN", /* 570 */
"\\FSPD", /* 600e/x, 770e, 770x */
@@ -231,6 +231,106 @@ struct ibm_thermal_sensors_struct {
s32 temp[IBMACPI_MAX_THERMAL_SENSORS];
};

+/*
+ * FAN ACCESS MODES
+ *
+ * IBMACPI_FAN_RD_ACPI_GFAN:
+ * ACPI GFAN method: returns fan level
+ *
+ * see IBMACPI_FAN_WR_ACPI_SFAN
+ * EC 0x2f not available if GFAN exists
+ *
+ * IBMACPI_FAN_WR_ACPI_SFAN:
+ * ACPI SFAN method: sets fan level, 0 (stop) to 7 (max)
+ *
+ * EC 0x2f might be available *for reading*, but never for writing.
+ *
+ * IBMACPI_FAN_WR_TPEC:
+ * ThinkPad EC register 0x2f (HFSP): fan control loop mode Supported
+ * on almost all ThinkPads
+ *
+ * Fan speed changes of any sort (including those caused by the
+ * disengaged mode) are usually done slowly by the firmware as the
+ * maximum ammount of fan duty cycle change per second seems to be
+ * limited.
+ *
+ * Reading is not available if GFAN exists.
+ * Writing is not available if SFAN exists.
+ *
+ * Bits
+ * 7 automatic mode engaged;
+ * (default operation mode of the ThinkPad)
+ * fan level is ignored in this mode.
+ * 6 disengage mode (takes precedence over bit 7);
+ * not available on all thinkpads. May disable
+ * the tachometer, and speeds up fan to 100% duty-cycle,
+ * which speeds it up far above the standard RPM
+ * levels. It is not impossible that it could cause
+ * hardware damage.
+ * 5-3 unused in some models. Extra bits for fan level
+ * in others, but still useless as all values above
+ * 7 map to the same speed as level 7 in these models.
+ * 2-0 fan level (0..7 usually)
+ * 0x00 = stop
+ * 0x07 = max (set when temperatures critical)
+ * Some ThinkPads may have other levels, see
+ * IBMACPI_FAN_WR_ACPI_FANS (X31/X40/X41)
+ *
+ * FIRMWARE BUG: on some models, EC 0x2f might not be initialized at
+ * boot. Apparently the EC does not intialize it, so unless ACPI DSDT
+ * does so, its initial value is meaningless (0x07).
+ *
+ * For firmware bugs, refer to:
+ * http://thinkwiki.org/wiki/Embedded_Controller_Firmware#Firmware_Issues
+ *
+ * ----
+ *
+ * ThinkPad EC register 0x84 (LSB), 0x85 (MSB):
+ * Main fan tachometer reading (in RPM)
+ *
+ * This register is present on all ThinkPads with a new-style EC, and
+ * it is known not to be present on the A21m/e, and T22, as there is
+ * something else in offset 0x84 according to the ACPI DSDT. Other
+ * ThinkPads from this same time period (and earlier) probably lack the
+ * tachometer as well.
+ *
+ * Unfortunately a lot of ThinkPads with new-style ECs but whose firwmare
+ * was never fixed by IBM to report the EC firmware version string
+ * probably support the tachometer (like the early X models), so
+ * detecting it is quite hard. We need more data to know for sure.
+ *
+ * FIRMWARE BUG: always read 0x84 first, otherwise incorrect readings
+ * might result.
+ *
+ * FIRMWARE BUG: when EC 0x2f bit 6 is set (disengaged mode), this
+ * register is not invalidated in ThinkPads that disable tachometer
+ * readings. Thus, the tachometer readings go stale.
+ *
+ * For firmware bugs, refer to:
+ * http://thinkwiki.org/wiki/Embedded_Controller_Firmware#Firmware_Issues
+ *
+ * IBMACPI_FAN_WR_ACPI_FANS:
+ * ThinkPad X31, X40, X41. Not available in the X60.
+ *
+ * FANS ACPI handle: takes three arguments: low speed, medium speed,
+ * high speed. ACPI DSDT seems to map these three speeds to levels
+ * as follows: STOP LOW LOW MED MED HIGH HIGH HIGH HIGH
+ * (this map is stored on FAN0..FAN8 as "0,1,1,2,2,3,3,3,3")
+ *
+ * The speeds are stored on handles
+ * (FANA:FAN9), (FANC:FANB), (FANE:FAND).
+ *
+ * There are three default speed sets, acessible as handles:
+ * FS1L,FS1M,FS1H; FS2L,FS2M,FS2H; FS3L,FS3M,FS3H
+ *
+ * ACPI DSDT switches which set is in use depending on various
+ * factors.
+ *
+ * IBMACPI_FAN_WR_TPEC is also available and should be used to
+ * command the fan. The X31/X40/X41 seems to have 8 fan levels,
+ * but the ACPI tables just mention level 7.
+ */
+
enum fan_status_access_mode {
IBMACPI_FAN_NONE = 0, /* No fan status or control */
IBMACPI_FAN_RD_ACPI_GFAN, /* Use ACPI GFAN */
@@ -1722,7 +1822,7 @@ static int fan_init(void)
/* all other models implement TP EC 0x2f control */

if (fans_handle) {
- /* X31, X40 */
+ /* X31, X40, X41 */
fan_control_access_mode =
IBMACPI_FAN_WR_ACPI_FANS;
fan_control_commands |=
@@ -1742,6 +1842,9 @@ static int fan_get_status(u8 *status)
{
u8 s;

+ /* TODO:
+ * Add IBMACPI_FAN_RD_ACPI_FANS ? */
+
switch (fan_status_access_mode) {
case IBMACPI_FAN_RD_ACPI_GFAN:
/* 570, 600e/x, 770e, 770x */
@@ -1950,6 +2053,9 @@ static int fan_write_cmd_speed(const cha
{
int speed;

+ /* TODO:
+ * Support speed <low> <medium> <high> ? */
+
if (sscanf(cmd, "speed %d", &speed) != 1)
return 0;