rt2x00: Avoid unnecessary uncached

Reading the TX desciptor words from coherent memory is always uncached
and potentially slow. Hence, don't read the TX descriptor prior to
writing it since we update all fields anyway.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800pci.c

@@ -619,11 +619,11 @@ static void rt2800pci_write_tx_desc(struct queue_entry *entry,
 	/*
 	 * Initialize TX descriptor
 	 */
-	rt2x00_desc_read(txd, 0, &word);
+	word = 0;
 	rt2x00_set_field32(&word, TXD_W0_SD_PTR0, skbdesc->skb_dma);
 	rt2x00_desc_write(txd, 0, word);
 
-	rt2x00_desc_read(txd, 1, &word);
+	word = 0;
 	rt2x00_set_field32(&word, TXD_W1_SD_LEN1, entry->skb->len);
 	rt2x00_set_field32(&word, TXD_W1_LAST_SEC1,
 			   !test_bit(ENTRY_TXD_MORE_FRAG, &txdesc->flags));
@@ -634,12 +634,12 @@ static void rt2800pci_write_tx_desc(struct queue_entry *entry,
 	rt2x00_set_field32(&word, TXD_W1_DMA_DONE, 0);
 	rt2x00_desc_write(txd, 1, word);
 
-	rt2x00_desc_read(txd, 2, &word);
+	word = 0;
 	rt2x00_set_field32(&word, TXD_W2_SD_PTR1,
 			   skbdesc->skb_dma + TXWI_DESC_SIZE);
 	rt2x00_desc_write(txd, 2, word);
 
-	rt2x00_desc_read(txd, 3, &word);
+	word = 0;
 	rt2x00_set_field32(&word, TXD_W3_WIV,
 			   !test_bit(ENTRY_TXD_ENCRYPT_IV, &txdesc->flags));
 	rt2x00_set_field32(&word, TXD_W3_QSEL, 2);