requiring DC_TX_ALIGN or DC_TX_COALESCE, which was previously done
in dc_start_locked(), into dc_encap().
o In dc_encap():
- If m_defrag() fails just drop the packet like other NIC drivers
do. This should only happen when there's a mbuf shortage, in which
case it was possible to end up with an IFQ full of packets which
couldn't be processed as they couldn't be defragmented as they
were taking up all the mbufs themselves. This includes adjusting
dc_start_locked() to not trying to prepend the mbuf (chain) if
dc_encap() has freed it.
- Likewise, if bus_dmamap_load_mbuf() fails as dc_dma_map_txbuf()
failed, free the mbuf possibly allocated by the above call to
m_defrag() and drop the packet.
o In dc_txeof():
- Don't clear IFF_DRV_OACTIVE unless there are at least 6 free TX
descriptors. Further down the road dc_encap() will bail if there
are only 5 or fewer free TX descriptors, causing dc_start_locked()
to abort and prepend the dequeued mbuf again so it makes no sense
to pretend we could process mbufs again when in fact we won't.
While at it replace this magic 5 with a macro DC_TX_LIST_RSVD.
- Just always assign idx to sc->dc_cdata.dc_tx_cons; it doesn't
make much sense to exclude the idx == sc->dc_cdata.dc_tx_cons
case.
o In dc_dma_map_txbuf() there's no need to set sc->dc_cdata.dc_tx_err
to error if the latter is != 0, bus_dmamap_load_mbuf() already
returns the same error value in that case anyway.
o For less overhead, convert to use bus_dmamap_load_mbuf_sg() for
loading RX buffers.
o Remove some banal and/or outdated comments.
Approved by: re (kensmith)
MFC after: 1 week
82a67a70a2