• Clemens Ladisch's avatar
    ALSA: usb-audio: prevent CH345 multiport output SysEx corruption · 1ca8b201
    Clemens Ladisch authored
    The CH345 USB MIDI chip has two output ports.  However, they are
    multiplexed through one pin, and the number of ports cannot be reduced
    even for hardware that implements only one connector, so for those
    devices, data sent to either port ends up on the same hardware output.
    This becomes a problem when both ports are used at the same time, as
    longer MIDI commands (such as SysEx messages) are likely to be
    interrupted by messages from the other port, and thus to get lost.
    
    It would not be possible for the driver to detect how many ports the
    device actually has, except that in practice, _all_ devices built with
    the CH345 have only one port.  So we can just ignore the device's
    descriptors, and hardcode one output port.
    Signed-off-by: default avatarClemens Ladisch <clemens@ladisch.de>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    1ca8b201
midi.c 67.3 KB