Re: [PATCH net v2] net: wwan: mhi_wwan_ctrl: send a DTR drop before it can be coalesced

[Peter Hunt <peter.hunt@opengear.com>]

Thanks for the review. This has since been applied to net, so for the
record:

[Medium] Drop lost when the transport refuses it: right, a drop that
hits a full UL ring (or a failed allocation) and is followed by a raise
within the 10ms retry still reaches the modem as just the raise. The
commit message calls this out, but the new comment overstates it.
Tracking an unsent drop until it is queued is roughly what v1 did, and
Loic found that too heavy for this case, so the flush stays best effort.

On the flush in stop(), a retry left armed after a failed attempt can
fire after mhi_unprepare_from_transfer(). That isn't new, v10 had no
flush in stop() at all, so the work could already run after the channel
stopped. The message goes out on the IP_CTRL channel, which is still
running, the AT channel only appears as dest_id. If the port is
reopened before the retry fires, the retry sends the latest state, i.e.
the raise from the reopen, so the modem ends up in the right state.

[Low] Stale comments: agreed. I'll send a comment-only patch for
net-next that says the drop flush is best effort, mentions it in the
dtr_mdmbits comment and drops "one attempt" from the remove() comment.