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-rw-r--r--Documentation/laptops/thinkpad-acpi.txt13
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index bd87682..6a58143 100644
--- a/Documentation/laptops/thinkpad-acpi.txt
+++ b/Documentation/laptops/thinkpad-acpi.txt
@@ -1097,6 +1097,18 @@ Volume control
procfs: /proc/acpi/ibm/volume
+NOTE: by default, the volume control interface operates in read-only
+mode, as it is supposed to be used for on-screen-display purposes.
+The read/write mode can be enabled through the use of the
+"volume_control=1" module parameter.
+
+NOTE: distros are urged to not enable volume_control by default, this
+should be done by the local admin only. The ThinkPad UI is for the
+console audio control to be done through the volume keys only, and for
+the desktop environment to just provide on-screen-display feedback.
+Software volume control should be done only in the main AC97/HDA
+mixer.
+
This feature allows volume control on ThinkPad models with a digital
volume knob (when available, not all models have it), as well as
mute/unmute control. The available commands are:
@@ -1465,3 +1477,4 @@ Sysfs interface changelog:
0x020600: Marker for backlight change event support.
0x020700: Support for mute-only mixers.
+ Volume control in read-only mode by default.