ACPI: thinkpad-acpi: document keymap gotcha's (v2)

Publish the requirements for keymap changes.  This is a documentation
change, only.

Currently, people look at the thinkpad-acpi default keymaps, and think:
"modifying this is a trivial thing, it can't break systems, and there are
keys defined for foo and bar, but the driver has them as KEY_RESERVED.
Must have been an oversight, let me change it."

And since they never get to see the bug reports, because they are not
really a part of the Linux ThinkPad users community (linux-thinkpad
mailinglist, thinkwiki wiki, thinkpad forums) and laptop users are slow
to complain to distros about any breakages...
Signed-off-by: NHenrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: NLen Brown <len.brown@intel.com>

drivers/misc/thinkpad_acpi.c

@@ -954,26 +954,67 @@ static struct attribute *hotkey_mask_attributes[] __initdata = {
 
 static int __init hotkey_init(struct ibm_init_struct *iibm)
 {
-
+	/* Requirements for changing the default keymaps:
+	 *
+	 * 1. Many of the keys are mapped to KEY_RESERVED for very
+	 *    good reasons.  Do not change them unless you have deep
+	 *    knowledge on the IBM and Lenovo ThinkPad firmware for
+	 *    the various ThinkPad models.  The driver behaves
+	 *    differently for KEY_RESERVED: such keys have their
+	 *    hot key mask *unset* in mask_recommended, and also
+	 *    in the initial hot key mask programmed into the
+	 *    firmware at driver load time, which means the firm-
+	 *    ware may react very differently if you change them to
+	 *    something else;
+	 *
+	 * 2. You must be subscribed to the linux-thinkpad and
+	 *    ibm-acpi-devel mailing lists, and you should read the
+	 *    list archives since 2007 if you want to change the
+	 *    keymaps.  This requirement exists so that you will
+	 *    know the past history of problems with the thinkpad-
+	 *    acpi driver keymaps, and also that you will be
+	 *    listening to any bug reports;
+	 *
+	 * 3. Do not send thinkpad-acpi specific patches directly to
+	 *    for merging, *ever*.  Send them to the linux-acpi
+	 *    mailinglist for comments.  Merging is to be done only
+	 *    through acpi-test and the ACPI maintainer.
+	 *
+	 * If the above is too much to ask, don't change the keymap.
+	 * Ask the thinkpad-acpi maintainer to do it, instead.
+	 */
 	static u16 ibm_keycode_map[] __initdata = {
 		/* Scan Codes 0x00 to 0x0B: ACPI HKEY FN+F1..F12 */
 		KEY_FN_F1,	KEY_FN_F2,	KEY_COFFEE,	KEY_SLEEP,
 		KEY_WLAN,	KEY_FN_F6, KEY_SWITCHVIDEOMODE, KEY_FN_F8,
 		KEY_FN_F9,	KEY_FN_F10,	KEY_FN_F11,	KEY_SUSPEND,
-		/* Scan codes 0x0C to 0x0F: Other ACPI HKEY hot keys */
+
+		/* Scan codes 0x0C to 0x1F: Other ACPI HKEY hot keys */
 		KEY_UNKNOWN,	/* 0x0C: FN+BACKSPACE */
 		KEY_UNKNOWN,	/* 0x0D: FN+INSERT */
 		KEY_UNKNOWN,	/* 0x0E: FN+DELETE */
+
+		/* brightness: firmware always reacts to them, unless
+		 * X.org did some tricks in the radeon BIOS scratch
+		 * registers of *some* models */
 		KEY_RESERVED,	/* 0x0F: FN+HOME (brightness up) */
-		/* Scan codes 0x10 to 0x1F: Extended ACPI HKEY hot keys */
 		KEY_RESERVED,	/* 0x10: FN+END (brightness down) */
+
+		/* Thinklight: firmware always react to it */
 		KEY_RESERVED,	/* 0x11: FN+PGUP (thinklight toggle) */
+
 		KEY_UNKNOWN,	/* 0x12: FN+PGDOWN */
 		KEY_ZOOM,	/* 0x13: FN+SPACE (zoom) */
+
+		/* Volume: firmware always react to it and reprograms
+		 * the built-in *extra* mixer.  Never map it to control
+		 * another mixer by default. */
 		KEY_RESERVED,	/* 0x14: VOLUME UP */
 		KEY_RESERVED,	/* 0x15: VOLUME DOWN */
 		KEY_RESERVED,	/* 0x16: MUTE */
+
 		KEY_VENDOR,	/* 0x17: Thinkpad/AccessIBM/Lenovo */
+
 		/* (assignments unknown, please report if found) */
 		KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN,
 		KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN,
@@ -983,20 +1024,37 @@ static int __init hotkey_init(struct ibm_init_struct *iibm)
 		KEY_FN_F1,	KEY_COFFEE,	KEY_BATTERY,	KEY_SLEEP,
 		KEY_WLAN,	KEY_FN_F6, KEY_SWITCHVIDEOMODE, KEY_FN_F8,
 		KEY_FN_F9,	KEY_FN_F10,	KEY_FN_F11,	KEY_SUSPEND,
-		/* Scan codes 0x0C to 0x0F: Other ACPI HKEY hot keys */
+
+		/* Scan codes 0x0C to 0x1F: Other ACPI HKEY hot keys */
 		KEY_UNKNOWN,	/* 0x0C: FN+BACKSPACE */
 		KEY_UNKNOWN,	/* 0x0D: FN+INSERT */
 		KEY_UNKNOWN,	/* 0x0E: FN+DELETE */
+
 		KEY_RESERVED,	/* 0x0F: FN+HOME (brightness up) */
-		/* Scan codes 0x10 to 0x1F: Extended ACPI HKEY hot keys */
 		KEY_RESERVED,	/* 0x10: FN+END (brightness down) */
+
 		KEY_RESERVED,	/* 0x11: FN+PGUP (thinklight toggle) */
+
 		KEY_UNKNOWN,	/* 0x12: FN+PGDOWN */
 		KEY_ZOOM,	/* 0x13: FN+SPACE (zoom) */
+
+		/* Volume: z60/z61, T60 (BIOS version?): firmware always
+		 * react to it and reprograms the built-in *extra* mixer.
+		 * Never map it to control another mixer by default.
+		 *
+		 * T60?, T61, R60?, R61: firmware and EC tries to send
+		 * these over the regular keyboard, so these are no-ops,
+		 * but there are still weird bugs re. MUTE, so do not
+		 * change unless you get test reports from all Lenovo
+		 * models.  May cause the BIOS to interfere with the
+		 * HDA mixer.
+		 */
 		KEY_RESERVED,	/* 0x14: VOLUME UP */
 		KEY_RESERVED,	/* 0x15: VOLUME DOWN */
 		KEY_RESERVED,	/* 0x16: MUTE */
+
 		KEY_VENDOR,	/* 0x17: Thinkpad/AccessIBM/Lenovo */
+
 		/* (assignments unknown, please report if found) */
 		KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN,
 		KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN,