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

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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>
This commit is contained in:
Dmitry Torokhov 2023-05-11 11:52:47 -07:00
parent c4c7eac8ee
commit f219050af0
1 changed files with 32 additions and 4 deletions
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36
drivers/input/serio/libps2.c
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@ -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;
}