USB: serial: mxuport: handle SEND_NEXT transmit flow control

The device uses a per-port SEND_NEXT request and event to pace
host-to-device transmission. During burn-in testing, sustained writes
without waiting for this event resulted in per-port buffer overflows and
data errors. The issue can be reproduced on existing G1 devices as well.

The driver initiates the protocol by setting the SEND_NEXT bit in a
bulk-out header and then stops submitting data for that port. The
firmware reports a SEND_NEXT event when the corresponding per-port
buffer is empty, at which point the driver resumes transmission.

Track the payload placed in bulk-out transfers for each port and set the
request bit when it reaches bulk_out_size. Use the generic write control
callbacks to hold further submissions until the event arrives and to
roll back the payload count and hold state if usb_submit_urb() fails.

Use bulk_out_size as a common threshold for all device families instead
of encoding their firmware buffer sizes in the driver.

Signed-off-by: Crescent Hsieh <crescentcy.hsieh@moxa.com>
Signed-off-by: Johan Hovold <johan@kernel.org>

0 files changed, 0 insertions, 0 deletions