This patch extends MIDI 2.0 function driver to add more proper support
for MIDI 1.0 interface.  Before this patch, the driver only exposes
the USB descriptor of a MIDI 1.0 interface in altset 0 while no actual
I/O is running for it.  This patch enables the actual I/O for the
altset 0; the backend UMP rawmidi is translated from/to the MIDI 1.0
USB commands.

For converting to USB MIDI 1.0 data protocol, a helper function is
copied from the existing f_midi driver, in addition to a few other UMP
Core helper functions.  For the MIDI 1.0 OUT (that is, input for
gadget), the incoming USB MIDI 1.0 packet is translated to UMP packets
via UMP Core helper, and tossed to the attached UMP rawmidi.  It's a
relatively straightforward.  OTOH, for MIDI 1.0 IN (i.e. output for
gadget), it's a bit more complex: we need to convert a source UMP
packet once to the standard MIDI 1.0 byte stream, and convert it again
to USB MIDI 1.0 packets, then send them out.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20230725062206.9674-5-tiwai@suse.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>