ACPI: thinkpad-acpi: add a safety net for TPEC fan control mode

The Linux ThinkPad community is not positive that all ThinkPads that do
HFSP EC fan control do implement full-speed and auto modes, some of the
earlier ones supporting HFSP might not.

If the EC ignores the AUTO or FULL-SPEED bits, it will pay attention to the
lower three bits that set the fan level.  And as thinkpad-acpi was leaving
these set to zero, it would stop(!) the fan, which is Not A Good Thing.

So, as a safety net, we now make sure to also set the fan level part of the
HFSP register to speed 7 for full-speed, and a minimum of speed 4 for auto
mode.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/drivers/misc/thinkpad_acpi.c b/drivers/misc/thinkpad_acpi.c
index a4d7ee472396..79abc6841e30 100644
--- a/drivers/misc/thinkpad_acpi.c
+++ b/drivers/misc/thinkpad_acpi.c
@@ -3185,6 +3185,13 @@ static int fan_set_level(int level)
                     ((level < 0) || (level > 7)))
                         return -EINVAL;
 
+                /* safety net should the EC not support AUTO
+                 * or FULLSPEED mode bits and just ignore them */
+                if (level & TP_EC_FAN_FULLSPEED)
+                        level |= 7;     /* safety min speed 7 */
+                else if (level & TP_EC_FAN_FULLSPEED)
+                        level |= 4;     /* safety min speed 4 */
+
                 if (!acpi_ec_write(fan_status_offset, level))
                         return -EIO;
                 else
@@ -3233,8 +3240,10 @@ static int fan_set_enable(void)
                         break;
 
                 /* Don't go out of emergency fan mode */
-                if (s != 7)
-                        s = TP_EC_FAN_AUTO;
+                if (s != 7) {
+                        s &= 0x07;
+                        s |= TP_EC_FAN_AUTO | 4; /* min fan speed 4 */
+                }
 
                 if (!acpi_ec_write(fan_status_offset, s))
                         rc = -EIO;
@@ -3252,8 +3261,7 @@ static int fan_set_enable(void)
                 s &= 0x07;
 
                 /* Set fan to at least level 4 */
-                if (s < 4)
-                        s = 4;
+                s |= 4;
 
                 if (!acpi_evalf(sfan_handle, NULL, NULL, "vd", s))
                         rc= -EIO;