thinkpad-acpi: support MUTE-only ThinkPads

Lenovo removed the extra mixer since the T61 and thereabouts.
Newer Lenovo models only have the mute gate function, and leave
the volume control to the HDA mixer.

Until a way to automatically query the firmware about its audio
control capabilities is discovered (there might not be any), use a
white/black list.

We will likely need to ask T60 (old and new model) and Z60/Z61 users
whether they have volume control to populate the black/white list.
Meanwhile, provide a volume_capabilities parameter that can be used to
override the defaults.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Lorne Applebaum <lorne.applebaum@gmail.com>
Cc: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 17 insertions, 2 deletions

diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index 96687d0106a9..bd87682103c1 100644
--- a/Documentation/laptops/thinkpad-acpi.txt
+++ b/Documentation/laptops/thinkpad-acpi.txt
@@ -1098,18 +1098,31 @@ Volume control
 procfs: /proc/acpi/ibm/volume
 
 This feature allows volume control on ThinkPad models with a digital
-volume knob, as well as mute/unmute control.  The available commands are:
+volume knob (when available, not all models have it), as well as
+mute/unmute control.  The available commands are:
 
         echo up   >/proc/acpi/ibm/volume
         echo down >/proc/acpi/ibm/volume
         echo mute >/proc/acpi/ibm/volume
+        echo unmute >/proc/acpi/ibm/volume
         echo 'level <level>' >/proc/acpi/ibm/volume
 
 The <level> number range is 0 to 14 although not all of them may be
 distinct. The unmute the volume after the mute command, use either the
-up or down command (the level command will not unmute the volume).
+up or down command (the level command will not unmute the volume), or
+the unmute command.
+
 The current volume level and mute state is shown in the file.
 
+You can use the volume_capabilities parameter to tell the driver
+whether your thinkpad has volume control or mute-only control:
+volume_capabilities=1 for mixers with mute and volume control,
+volume_capabilities=2 for mixers with only mute control.
+
+If the driver misdetects the capabilities for your ThinkPad model,
+please report this to ibm-acpi-devel@lists.sourceforge.net, so that we
+can update the driver.
+
 There are two strategies for volume control.  To select which one
 should be used, use the volume_mode module parameter: volume_mode=1
 selects EC mode, and volume_mode=3 selects EC mode with NVRAM backing
@@ -1450,3 +1463,5 @@ Sysfs interface changelog:
                 is deprecated and marked for removal.
 
 0x020600:       Marker for backlight change event support.
+
+0x020700:       Support for mute-only mixers.