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.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>