On 5 Jan, silby_at_silby.com wrote: >> I just took a closer look at the busdma diff, and this change to >> dc_txeof() looks very suspicious: >> >> - if (!(cur_tx->dc_ctl & DC_TXCTL_LASTFRAG) || >> + if (!(cur_tx->dc_ctl & DC_TXCTL_FIRSTFRAG) || >> cur_tx->dc_ctl & DC_TXCTL_SETUP) { > > I'm current checking e-mail via a webmail interface and I haven't had time > to check over your later posts, but I thought I'd note that the change > above _is_ busdma related; one subtle change in the busdma code was that > the mbuf is now linked to the first fragment in the chain, whereas before > it was linked to the last fragment. So, the change does make sense on the > surface, although I wouldn't be surprised if it broke something subtle. Hmn, in that case skipping the "if" block if either DC_TXCTL_LASTFRAG is set or if DC_TXCTL_FIRSTFRAG is set would be appropriate. Then we would need to execute the code fragment: if (txstat & DC_TXSTAT_ERRSUM) { ifp->if_oerrors++; if (txstat & DC_TXSTAT_EXCESSCOLL) ifp->if_collisions++; if (txstat & DC_TXSTAT_LATECOLL) ifp->if_collisions++; if (!(txstat & DC_TXSTAT_UNDERRUN)) { dc_init(sc); return; } } ifp->if_collisions += (txstat & DC_TXSTAT_COLLCNT) >> 3; if the DC_TXCTL_LASTFRAG is set and execute the code fragment ifp->if_opackets++; if (sc->dc_cdata.dc_tx_chain[idx] != NULL) { m_freem(sc->dc_cdata.dc_tx_chain[idx]); sc->dc_cdata.dc_tx_chain[idx] = NULL; } if the DC_TXCTL_FIRSTFRAGMENT flag is set. I think this would introduce another subtle bug. I'm pretty sure that the chip clears the DC_TXSTAT_OWN bit after it does the DMA for each descriptor, so freeing the mbuf chain as soon as we see the DC_TXSTAT_OWN bit go away on the first descriptor may free the mbuf chain before the chip has copied the entire frame. I think it would be better to revert the change to dc_txeof() and to hang the mbuf chain off the last descriptor.Received on Mon Jan 05 2004 - 07:13:27 UTC
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