2 files changed, 55 insertions, 5 deletions

diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index bd87682103c1..6a5814330e51 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.
diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c
index 4d909d5a0340..2d74926913d2 100644
--- a/drivers/platform/x86/thinkpad_acpi.c
+++ b/drivers/platform/x86/thinkpad_acpi.c
@@ -311,6 +311,7 @@ static struct {
 
 static struct {
         u16 hotkey_mask_ff:1;
+        u16 volume_ctrl_forbidden:1;
 } tp_warned;
 
 struct thinkpad_id_data {
@@ -6434,6 +6435,7 @@ static enum tpacpi_volume_access_mode volume_mode =
         TPACPI_VOL_MODE_MAX;
 
 static enum tpacpi_volume_capabilities volume_capabilities;
+static int volume_control_allowed;
 
 /*
  * Used to syncronize writers to TP_EC_AUDIO and
@@ -6449,6 +6451,8 @@ static void tpacpi_volume_checkpoint_nvram(void)
 
         if (volume_mode != TPACPI_VOL_MODE_ECNVRAM)
                 return;
+        if (!volume_control_allowed)
+                return;
 
         vdbg_printk(TPACPI_DBG_MIXER,
                 "trying to checkpoint mixer state to NVRAM...\n");
@@ -6691,6 +6695,12 @@ static int __init volume_init(struct ibm_init_struct *iibm)
                         "mute is supported, volume control is %s\n",
                         str_supported(!tp_features.mixer_no_level_control));
 
+        printk(TPACPI_INFO
+                "Console audio control enabled, mode: %s\n",
+                (volume_control_allowed) ?
+                        "override (read/write)" :
+                        "monitor (read only)");
+
         return 0;
 }
 
@@ -6711,11 +6721,16 @@ static int volume_read(char *p)
                 len += sprintf(p + len, "mute:\t\t%s\n",
                                 onoff(status, TP_EC_AUDIO_MUTESW));
 
-                len += sprintf(p + len, "commands:\tunmute, mute\n");
-                if (!tp_features.mixer_no_level_control) {
-                        len += sprintf(p + len, "commands:\tup, down\n");
-                        len += sprintf(p + len, "commands:\tlevel <level>"
-                               " (<level> is 0-%d)\n", TP_EC_VOLUME_MAX);
+                if (volume_control_allowed) {
+                        len += sprintf(p + len, "commands:\tunmute, mute\n");
+                        if (!tp_features.mixer_no_level_control) {
+                                len += sprintf(p + len,
+                                               "commands:\tup, down\n");
+                                len += sprintf(p + len,
+                                               "commands:\tlevel <level>"
+                                               " (<level> is 0-%d)\n",
+                                               TP_EC_VOLUME_MAX);
+                        }
                 }
         }
 
@@ -6730,6 +6745,23 @@ static int volume_write(char *buf)
         char *cmd;
         int rc;
 
+        /*
+         * We do allow volume control at driver startup, so that the
+         * user can set initial state through the volume=... parameter hack.
+         */
+        if (!volume_control_allowed && tpacpi_lifecycle != TPACPI_LIFE_INIT) {
+                if (unlikely(!tp_warned.volume_ctrl_forbidden)) {
+                        tp_warned.volume_ctrl_forbidden = 1;
+                        printk(TPACPI_NOTICE
+                                "Console audio control in monitor mode, "
+                                "changes are not allowed.\n");
+                        printk(TPACPI_NOTICE
+                                "Use the volume_control=1 module parameter "
+                                "to enable volume control\n");
+                }
+                return -EPERM;
+        }
+
         rc = volume_get_status(&s);
         if (rc < 0)
                 return rc;
@@ -8515,6 +8547,11 @@ MODULE_PARM_DESC(volume_capabilities,
                  "Selects the mixer capabilites: "
                  "0=auto, 1=volume and mute, 2=mute only");
 
+module_param_named(volume_control, volume_control_allowed, bool, 0444);
+MODULE_PARM_DESC(volume_control,
+                 "Enables software override for the console audio "
+                 "control when true");
+
 #define TPACPI_PARAM(feature) \
         module_param_call(feature, set_ibm_param, NULL, NULL, 0); \
         MODULE_PARM_DESC(feature, "Simulates thinkpad-acpi procfs command " \