iwm: rx dma init fix

[Stefan Sperling]

According to a comment in iwlwifi:

 * Clearing FH_MEM_RCSR_CHNL0_CONFIG_REG to 0 turns off Rx DMA.
 * Driver should poll FH_MEM_RSSR_RX_STATUS_REG for
 * FH_RSSR_CHNL0_RX_STATUS_CHNL_IDLE (bit 24) before continuing.

We missed polling this bit in the init code path. Probably harmless,
but can be fixed in a simple way by splitting iwm_reset_rx_ring()
into two functions.

Index: if_iwm.c
===================================================================
RCS file: /cvs/src/sys/dev/pci/if_iwm.c,v
retrieving revision 1.79
diff -u -p -r1.79 if_iwm.c
--- if_iwm.c    13 Apr 2016 10:34:32 -0000      1.79
+++ if_iwm.c    17 May 2016 16:20:16 -0000
@@ -235,6 +235,7 @@ void        iwm_free_kw(struct iwm_softc *);
 int    iwm_alloc_ict(struct iwm_softc *);
 void   iwm_free_ict(struct iwm_softc *);
 int    iwm_alloc_rx_ring(struct iwm_softc *, struct iwm_rx_ring *);
+void   iwm_disable_rx_dma(struct iwm_softc *);
 void   iwm_reset_rx_ring(struct iwm_softc *, struct iwm_rx_ring *);
 void   iwm_free_rx_ring(struct iwm_softc *, struct iwm_rx_ring *);
 int    iwm_alloc_tx_ring(struct iwm_softc *, struct iwm_tx_ring *, int);
@@ -1050,7 +1051,7 @@ fail:     iwm_free_rx_ring(sc, ring);
 }
 
 void
-iwm_reset_rx_ring(struct iwm_softc *sc, struct iwm_rx_ring *ring)
+iwm_disable_rx_dma(struct iwm_softc *sc)
 {
        int ntries;
 
@@ -1064,6 +1065,11 @@ iwm_reset_rx_ring(struct iwm_softc *sc, 
                }
                iwm_nic_unlock(sc);
        }
+}
+
+void
+iwm_reset_rx_ring(struct iwm_softc *sc, struct iwm_rx_ring *ring)
+{
        ring->cur = 0;
        bus_dmamap_sync(sc->sc_dmat, ring->stat_dma.map, 0,
            ring->stat_dma.size, BUS_DMASYNC_PREWRITE);
@@ -1537,6 +1543,7 @@ iwm_stop_device(struct iwm_softc *sc)
                }
                iwm_nic_unlock(sc);
        }
+       iwm_disable_rx_dma(sc);
 
        /* Stop RX ring. */
        iwm_reset_rx_ring(sc, &sc->rxq);
@@ -1631,7 +1638,7 @@ iwm_nic_rx_init(struct iwm_softc *sc)
        memset(sc->rxq.stat, 0, sizeof(*sc->rxq.stat));
 
        /* stop DMA */
-       IWM_WRITE(sc, IWM_FH_MEM_RCSR_CHNL0_CONFIG_REG, 0);
+       iwm_disable_rx_dma(sc);
        IWM_WRITE(sc, IWM_FH_MEM_RCSR_CHNL0_RBDCB_WPTR, 0);
        IWM_WRITE(sc, IWM_FH_MEM_RCSR_CHNL0_FLUSH_RB_REQ, 0);
        IWM_WRITE(sc, IWM_FH_RSCSR_CHNL0_RDPTR, 0);