5.2-RC oerrs and collisions on dc0

Maxime Henrion mux at freebsd.org
Mon Jan 5 10:34:47 PST 2004

Don Lewis wrote:
> I just took a closer look at the busdma diff, and this change to
> dc_txeof() looks very suspicious:
> @@ -2663,7 +2809,7 @@
>                 if (txstat & DC_TXSTAT_OWN)
>                         break;
> -               if (!(cur_tx->dc_ctl & DC_TXCTL_LASTFRAG) ||
> +               if (!(cur_tx->dc_ctl & DC_TXCTL_FIRSTFRAG) ||
>                     cur_tx->dc_ctl & DC_TXCTL_SETUP) {
>                         if (cur_tx->dc_ctl & DC_TXCTL_SETUP) {
>                                 /*
> The code in the "if" block ends with a "continue" which will cause the
> error handling code to be skipped if the "if" condition is true.  I'm
> pretty sure that the error status bits are only set in the last
> descriptor for the frame, so we want to execute the "continue" unless
> the DC_TXCTL_LASTFRAG bit is set.
> Try reverting this part of the busdma change.

I think you actually found the culprit, though fixing this is not as
simple as reverting this line.  I changed the check to
DC_TXCTL_FIRSTFRAG because that's the descriptor which will have a link
to the mbuf, while it was previously done for the LASTFRAG descriptor.
However, I didn't think about the code flow enough it seems.  If you
don't have a fix for this soon, I should be able to do it pretty easily,
assuming I find the time.


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