Date: Tue, 21 Oct 2003 09:29:02 -0700 (PDT) From: Sam Leffler <sam@FreeBSD.org> To: Perforce Change Reviews <perforce@freebsd.org> Subject: PERFORCE change 40099 for review Message-ID: <200310211629.h9LGT2BF086334@repoman.freebsd.org>
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http://perforce.freebsd.org/chv.cgi?CH=40099 Change 40099 by sam@sam_ebb on 2003/10/21 09:28:45 terminate the rx descriptor list with a self-linked entry so high phy error rates don't cause rx overruns Affected files ... .. //depot/projects/netperf/sys/dev/ath/if_ath.c#27 edit Differences ... ==== //depot/projects/netperf/sys/dev/ath/if_ath.c#27 (text+ko) ==== @@ -1544,9 +1544,23 @@ } bus_dmamap_sync(sc->sc_dmat, bf->bf_dmamap, BUS_DMASYNC_PREREAD); - /* setup descriptors */ + /* + * Setup descriptors. For receive we always terminate + * the descriptor list with a self-linked entry so we'll + * not get overrun under high load (as can happen with a + * 5212 when ANI processing enables PHY errors). + * + * To insure the last descriptor is self-linked we create + * each descriptor as self-linked and add it to the end. As + * each additional descriptor is added the previous self-linked + * entry is ``fixed'' naturally. This should be safe even + * if DMA is happening. When processing RX interrupts we + * never remove/process the last, self-linked, entry on the + * descriptor list. This insures the hardware always has + * someplace to write a new frame. + */ ds = bf->bf_desc; - ds->ds_link = 0; + ds->ds_link = bf->bf_daddr; /* link to self */ ds->ds_data = bf->bf_segs[0].ds_addr; ath_hal_setuprxdesc(ah, ds , m->m_len /* buffer size */ @@ -1584,12 +1598,16 @@ if_printf(ifp, "ath_rx_proc: no buffer!\n"); break; } + ds = bf->bf_desc; + if (ds->ds_link == bf->bf_daddr) { + /* NB: never process the self-linked entry at the end */ + break; + } m = bf->bf_m; if (m == NULL) { /* NB: shouldn't happen */ if_printf(ifp, "ath_rx_proc: no mbuf!\n"); continue; } - ds = bf->bf_desc; status = ath_hal_rxprocdesc(ah, ds); #ifdef AR_DEBUG if (ath_debug > 1)
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