[IOAT]: ioatdma needs to to play nice in a multi-dma-client world

Now that the DMA engine has a multi-client interface, fix the ioatdma
driver to play along. At the same time, remove a couple of unnecessary
reads and writes.

Signed-off-by: Shannon Nelson <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/dma/ioatdma.c

···
 	int i;
 	LIST_HEAD(tmp_list);
 
-	/*
-	 * In-use bit automatically set by reading chanctrl
-	 * If 0, we got it, if 1, someone else did
-	 */
-	chanctrl = readw(ioat_chan->reg_base + IOAT_CHANCTRL_OFFSET);
-	if (chanctrl & IOAT_CHANCTRL_CHANNEL_IN_USE)
-		return -EBUSY;
+	/* have we already been set up? */
+	if (!list_empty(&ioat_chan->free_desc))
+		return INITIAL_IOAT_DESC_COUNT;
 
         /* Setup register to interrupt and write completion status on error */
-	chanctrl = IOAT_CHANCTRL_CHANNEL_IN_USE |
-		IOAT_CHANCTRL_ERR_INT_EN |
+	chanctrl = IOAT_CHANCTRL_ERR_INT_EN |
 		IOAT_CHANCTRL_ANY_ERR_ABORT_EN |
 		IOAT_CHANCTRL_ERR_COMPLETION_EN;
         writew(chanctrl, ioat_chan->reg_base + IOAT_CHANCTRL_OFFSET);
···
 			in_use_descs - 1);
 
 	ioat_chan->last_completion = ioat_chan->completion_addr = 0;
-
-	/* Tell hw the chan is free */
-	chanctrl = readw(ioat_chan->reg_base + IOAT_CHANCTRL_OFFSET);
-	chanctrl &= ~IOAT_CHANCTRL_CHANNEL_IN_USE;
-	writew(chanctrl, ioat_chan->reg_base + IOAT_CHANCTRL_OFFSET);
 }
 
 static struct dma_async_tx_descriptor *