Input: libps2 - do not discard non-ack bytes when controlling LEDs

Upon receiving a PS/2 command the device and controller are supposed to
stop sending normal data (scancodes or movement packets) and instead
immediately start delivering ACK/NAK and command response. Unfortunately
often EC has an output buffer which may contain latched data by the time
the EC receives a command from the host. The kernel used to ignore such
data, but that may cause "stuck" keys if the data dropped happens to be a
break code or a part of a break code. This occasionally happens, for
example, on Chromebooks when the kernel tries to toggle CapsLock LED on
a keyboard while user releases Alt+Search keyboard shortcut.

Fix this by passing the first non-ACK byte to the normal handler for a
handful of PS/2 commands that are expected to be used during normal device
operation (as opposed to probe/configuration time).

Reviewed-by: Raul E Rangel <rrangel@chromium.org>
Link: https://lore.kernel.org/r/20230511185252.386941-8-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

diff --git a/drivers/input/serio/libps2.c b/drivers/input/serio/libps2.c
index 7c5fc85..6d78a1f 100644 (file)
--- a/drivers/input/serio/libps2.c
+++ b/drivers/input/serio/libps2.c
@@ -21,7 +21,10 @@
 
 #define PS2_CMD_SETSCALE11     0x00e6
 #define PS2_CMD_SETRES         0x10e8
+#define PS2_CMD_EX_SETLEDS     0x20eb
+#define PS2_CMD_SETLEDS                0x10ed
 #define PS2_CMD_GETID          0x02f2
+#define PS2_CMD_SETREP         0x10f3 /* Set repeat rate/set report rate */
 #define PS2_CMD_RESET_BAT      0x02ff
 
 #define PS2_RET_BAT            0xaa
@@ -35,6 +38,7 @@
 #define PS2_FLAG_CMD1          BIT(2)  /* Waiting for the first byte of command response */
 #define PS2_FLAG_WAITID                BIT(3)  /* Command executing is GET ID */
 #define PS2_FLAG_NAK           BIT(4)  /* Last transmission was NAKed */
+#define PS2_FLAG_PASS_NOACK    BIT(5)  /* Pass non-ACK byte to receive handler */
 
 static int ps2_do_sendbyte(struct ps2dev *ps2dev, u8 byte,
                           unsigned int timeout, unsigned int max_attempts)
@@ -281,9 +285,28 @@ int __ps2_command(struct ps2dev *ps2dev, u8 *param, unsigned int command)
 
        serio_pause_rx(ps2dev->serio);
 
-       /* Some mice do not ACK the "get ID" command, prepare to handle this. */
-       ps2dev->flags = command == PS2_CMD_GETID ? PS2_FLAG_WAITID : 0;
        ps2dev->cmdcnt = receive;
+
+       switch (command) {
+       case PS2_CMD_GETID:
+               /*
+                * Some mice do not ACK the "get ID" command, prepare to
+                * handle this.
+                */
+               ps2dev->flags = PS2_FLAG_WAITID;
+               break;
+
+       case PS2_CMD_SETLEDS:
+       case PS2_CMD_EX_SETLEDS:
+       case PS2_CMD_SETREP:
+               ps2dev->flags = PS2_FLAG_PASS_NOACK;
+               break;
+
+       default:
+               ps2dev->flags = 0;
+               break;
+       }
+
        if (receive) {
                /* Indicate that we expect response to the command. */
                ps2dev->flags |= PS2_FLAG_CMD | PS2_FLAG_CMD1;
@@ -512,14 +535,19 @@ static void ps2_handle_ack(struct ps2dev *ps2dev, u8 data)
                 * Do not signal errors if we get unexpected reply while
                 * waiting for an ACK to the initial (first) command byte:
                 * the device might not be quiesced yet and continue
-                * delivering data.
+                * delivering data. For certain commands (such as set leds and
+                * set repeat rate) that can be used during normal device
+                * operation, we even pass this data byte to the normal receive
+                * handler.
                 * Note that we reset PS2_FLAG_WAITID flag, so the workaround
                 * for mice not acknowledging the Get ID command only triggers
                 * on the 1st byte; if device spews data we really want to see
                 * a real ACK from it.
                 */
                dev_dbg(&ps2dev->serio->dev, "unexpected %#02x\n", data);
-               ps2dev->flags &= ~PS2_FLAG_WAITID;
+               if (ps2dev->flags & PS2_FLAG_PASS_NOACK)
+                       ps2dev->receive_handler(ps2dev, data);
+               ps2dev->flags &= ~(PS2_FLAG_WAITID | PS2_FLAG_PASS_NOACK);
                return;
        }