When using the serial framework buffer, if the buffer is full, excess
data is cached in the usb req buffer. The CDCACM driver doesn't know
when the upper layer will read data from the serial buffer, so it
needs to periodically check if the cached data can be put into the
serial buffer. However, when using zero-copy, each usb req buffer
needs to be completely read before actively switching to the next
req buffer, so the timer is not needed to assist to query.
Signed-off-by: yangsong8 <yangsong8@xiaomi.com>
yangsong8
ae39301416