[PATCH v2] Input: CM109: Fix handling of volume and mute buttons

[Florian Euchner <florian.euchner@gmail.com>]

The CM109 driver reported key press events of volume up / down and
record / playback mute buttons, but no release events. Report those events
properly by handling volume and mute keys seperately. For the record and
playback mute buttons, only presses are registered by the CM109, therefore
simulate press-n-release. This fixes the volume control buttons of various
USB headsets.

Signed-off-by: Florian Euchner <florian.euchner@gmail.com>
---
Thank you very much for your response to my first patch, Dmitry.
I didn't realize input_report_key already does all of the logic to
make sure keypresses are not reported twice, which made my code more
complicated than it had to be. I have applied your code with some
adjustments:
* The for loop should only count to 4, not to 8. There are only four keys,
otherwise this would cause reading outside the bounds of the keymap[] array
and bits 4-7 of HID_IR0 are not used for keys according to the datasheet.
* The RECORD_MUTE key should mute the microphone, not the speaker.
* There only need to be 15 slots in the keymap for special keys since
"no special key pressed" is not a valid combination anymore.

I hope those adjustments make sense.

 drivers/input/misc/cm109.c | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/drivers/input/misc/cm109.c b/drivers/input/misc/cm109.c
index 9365535..ee1bedd 100644
--- a/drivers/input/misc/cm109.c
+++ b/drivers/input/misc/cm109.c
@@ -76,8 +76,8 @@ enum {
 
 	BUZZER_ON = 1 << 5,
 
-	/* up to 256 normal keys, up to 16 special keys */
-	KEYMAP_SIZE = 256 + 16,
+	/* up to 256 normal keys, up to 15 special key combinations */
+	KEYMAP_SIZE = 256 + 15,
 };
 
 /* CM109 protocol packet */
@@ -139,7 +139,7 @@ static unsigned short special_keymap(int code)
 {
 	if (code > 0xff) {
 		switch (code - 0xff) {
-		case RECORD_MUTE:	return KEY_MUTE;
+		case RECORD_MUTE:	return KEY_MICMUTE;
 		case PLAYBACK_MUTE:	return KEY_MUTE;
 		case VOLUME_DOWN:	return KEY_VOLUMEDOWN;
 		case VOLUME_UP:		return KEY_VOLUMEUP;
@@ -312,6 +312,32 @@ static void report_key(struct cm109_dev *dev, int key)
 	input_sync(idev);
 }
 
+/*
+ * Converts data of special key presses (volume, mute) into events
+ * for the input subsystem, sends press-n-release for mute keys.
+ */
+static void cm109_report_special(struct cm109_dev *dev)
+{
+	static const u8 autorelease = RECORD_MUTE | PLAYBACK_MUTE;
+	struct input_dev *idev = dev->idev;
+	u8 data = dev->irq_data->byte[HID_IR0];
+	unsigned short keycode;
+	int i;
+
+	for (i = 0; i < 4; i++) {
+		keycode = dev->keymap[0xff + BIT(i)];
+		if (keycode == KEY_RESERVED)
+			continue;
+
+		input_report_key(idev, keycode, data & BIT(i));
+		if (data & autorelease & BIT(i)) {
+			input_sync(idev);
+			input_report_key(idev, keycode, 0);
+		}
+	}
+	input_sync(idev);
+}
+
 /******************************************************************************
  * CM109 usb communication interface
  *****************************************************************************/
@@ -357,10 +383,7 @@ static void cm109_urb_irq_callback(struct urb *urb)
 	}
 
 	/* Special keys */
-	if (dev->irq_data->byte[HID_IR0] & 0x0f) {
-		const int code = (dev->irq_data->byte[HID_IR0] & 0x0f);
-		report_key(dev, dev->keymap[0xff + code]);
-	}
+	cm109_report_special(dev);
 
 	/* Scan key column */
 	if (dev->keybit == 0xf) {
-- 
2.8.2