iwlwifi: use Rx single frame mode (one Rx frame per RB)

The RCSR default value for single frame mode is off (a RB contains more than
one frames). But the driver assumes single frame mode apparently. This patch
enables single frame mode for the hardware. It also adds a BUG_ON to make sure
the allocated skb satisfies the hardware alignment requirement and removes
a useless check.
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-fh.h

@@ -266,6 +266,8 @@
 #define FH_RCSR_CHNL0_RX_CONFIG_IRQ_DEST_NO_INT_VAL    (0x00000000)
 #define FH_RCSR_CHNL0_RX_CONFIG_IRQ_DEST_INT_HOST_VAL  (0x00001000)
 
+#define FH_RCSR_CHNL0_RX_CONFIG_SINGLE_FRAME	(0x00008000)
+
 
 /**
  * Rx Shared Status Registers (RSSR)

drivers/net/wireless/iwlwifi/iwl-rx.c

@@ -218,8 +218,7 @@ int iwl_rx_queue_restock(struct iwl_priv *priv)
 
 	/* If we've added more space for the firmware to place data, tell it.
 	 * Increment device's write pointer in multiples of 8. */
-	if ((write != (rxq->write & ~0x7))
-	    || (abs(rxq->write - rxq->read) > 7)) {
+	if (write != (rxq->write & ~0x7)) {
 		spin_lock_irqsave(&rxq->lock, flags);
 		rxq->need_update = 1;
 		spin_unlock_irqrestore(&rxq->lock, flags);
@@ -440,6 +439,7 @@ int iwl_rx_init(struct iwl_priv *priv, struct iwl_rx_queue *rxq)
 			   FH_RCSR_RX_CONFIG_CHNL_EN_ENABLE_VAL |
 			   FH_RCSR_CHNL0_RX_IGNORE_RXF_EMPTY |
 			   FH_RCSR_CHNL0_RX_CONFIG_IRQ_DEST_INT_HOST_VAL |
+			   FH_RCSR_CHNL0_RX_CONFIG_SINGLE_FRAME |
 			   rb_size|
 			   (rb_timeout << FH_RCSR_RX_CONFIG_REG_IRQ_RBTH_POS)|
 			   (rfdnlog << FH_RCSR_RX_CONFIG_RBDCB_SIZE_POS));