To be compatible with the previous method, add a buf between cdcacm
and serial. Because when using usbreqbuf directly as the buf of serial,
the amount of data sent may be insufficient due to the limit of the
number of reqs. For example, when the number of reqs is 4, the number
of data send through cdcacm is 5, and each data is a separate USB
packet, if the host does not read in time, resulting in blocking send.
Signed-off-by: yangsong8 <yangsong8@xiaomi.com>
yangsong8
e8f9570ffd