If an option descriptor has been sent on a queue but not followed by a
packet, there will have been no completion event, so the read and write
counts won't match and we'll think we can't do PIO. This combines with
the fact that we have two TX queues (for en/disable checksum offload),
and that both must be empty for PIO to happen.
This patch adds a separate "packet_write_count" that tracks the most
recent write_count we expect to see a completion event for; this excludes
option descriptors but _includes_ PIO descriptors (even though they look
like option descriptors). This is then used, rather than write_count,
in efx_nic_tx_is_empty().
We only bother to maintain packet_write_count on EF10, since on Siena
(a) there are no option descriptors and it always equals write_count, and
(b) there's no PIO, so we don't need it anyway.
Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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