i2c: at91: enable probe deferring on dma channel request

If dma controller is not probed, defer i2c probe.

Signed-off-by: Ludovic Desroches <[e-mail]>
Reviewed-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/busses/i2c-at91.c

···
 	slave_config.dst_maxburst = 1;
 	slave_config.device_fc = false;
 
-	dma->chan_tx = dma_request_slave_channel(dev->dev, "tx");
-	if (!dma->chan_tx) {
-		dev_err(dev->dev, "can't get a DMA channel for tx\n");
-		ret = -EBUSY;
+	dma->chan_tx = dma_request_slave_channel_reason(dev->dev, "tx");
+	if (IS_ERR(dma->chan_tx)) {
+		ret = PTR_ERR(dma->chan_tx);
+		dma->chan_tx = NULL;
 		goto error;
 	}
 
-	dma->chan_rx = dma_request_slave_channel(dev->dev, "rx");
-	if (!dma->chan_rx) {
-		dev_err(dev->dev, "can't get a DMA channel for rx\n");
-		ret = -EBUSY;
+	dma->chan_rx = dma_request_slave_channel_reason(dev->dev, "rx");
+	if (IS_ERR(dma->chan_rx)) {
+		ret = PTR_ERR(dma->chan_rx);
+		dma->chan_rx = NULL;
 		goto error;
 	}
 
···
 	sg_init_table(&dma->sg, 1);
 	dma->buf_mapped = false;
 	dma->xfer_in_progress = false;
+	dev->use_dma = true;
 
 	dev_info(dev->dev, "using %s (tx) and %s (rx) for DMA transfers\n",
 		 dma_chan_name(dma->chan_tx), dma_chan_name(dma->chan_rx));
···
 	return ret;
 
 error:
-	dev_info(dev->dev, "can't use DMA\n");
+	if (ret != -EPROBE_DEFER)
+		dev_info(dev->dev, "can't use DMA, error %d\n", ret);
 	if (dma->chan_rx)
 		dma_release_channel(dma->chan_rx);
 	if (dma->chan_tx)
···
 	clk_prepare_enable(dev->clk);
 
 	if (dev->dev->of_node) {
-		if (at91_twi_configure_dma(dev, phy_addr) == 0)
-			dev->use_dma = true;
+		rc = at91_twi_configure_dma(dev, phy_addr);
+		if (rc == -EPROBE_DEFER)
+			return rc;
 	}
 
 	rc = of_property_read_u32(dev->dev->of_node, "clock-frequency",