The Tx descriptors have 20 "scatter-gather" slots, but two of those
are used to transfer the command, so only 18 remain for the actual
packet data. So limit the number of dma segments to IWM_NUM_OF_TBS - 2.
We use the same approach in iwn(4), except that there only one slot is
used for the command, so it uses IWN_MAX_SCATTER - 1.
I suspect that this bug is responsible for the
iwm0: hardware error, stopping device
errors I sometimes see when we listing long directories when ssh'ed in
over iwm(4). We all know ssh loves creating long fragmented mbuf
lists.
ok?
Index: if_iwm.c
===================================================================
RCS file: /cvs/src/sys/dev/pci/if_iwm.c,v
retrieving revision 1.40
diff -u -p -r1.40 if_iwm.c
--- if_iwm.c 21 May 2015 22:13:55 -0000 1.40
+++ if_iwm.c 21 May 2015 22:31:46 -0000
@@ -1113,7 +1113,8 @@ iwm_alloc_tx_ring(struct iwm_softc *sc,
paddr += sizeof(struct iwm_device_cmd);
error = bus_dmamap_create(sc->sc_dmat, MCLBYTES,
- IWM_NUM_OF_TBS, MCLBYTES, 0, BUS_DMA_NOWAIT, &data->map);
+ IWM_NUM_OF_TBS - 2, MCLBYTES, 0, BUS_DMA_NOWAIT,
+ &data->map);
if (error != 0) {
printf("%s: could not create TX buf DMA map\n",
DEVNAME(sc));
goto fail;
