mtd: rawnand: sunxi: Use dma_request_chan() instead dma_request_slave_channel()

dma_request_slave_channel() is a wrapper on top of dma_request_chan()
eating up the error code.

By using dma_request_chan() directly the driver can support deferred
probing against DMA.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200227123749.24064-5-peter.ujfalusi@ti.com

drivers/mtd/nand/raw/sunxi_nand.c

@@ -2123,8 +2123,16 @@ static int sunxi_nfc_probe(struct platform_device *pdev)
 	if (ret)
 		goto out_ahb_reset_reassert;
 
-	nfc->dmac = dma_request_slave_channel(dev, "rxtx");
-	if (nfc->dmac) {
+	nfc->dmac = dma_request_chan(dev, "rxtx");
+	if (IS_ERR(nfc->dmac)) {
+		ret = PTR_ERR(nfc->dmac);
+		if (ret == -EPROBE_DEFER)
+			goto out_ahb_reset_reassert;
+
+		/* Ignore errors to fall back to PIO mode */
+		dev_warn(dev, "failed to request rxtx DMA channel: %d\n", ret);
+		nfc->dmac = NULL;
+	} else {
 		struct dma_slave_config dmac_cfg = { };
 
 		dmac_cfg.src_addr = r->start + nfc->caps->reg_io_data;
@@ -2138,9 +2146,6 @@ static int sunxi_nfc_probe(struct platform_device *pdev)
 		if (nfc->caps->extra_mbus_conf)
 			writel(readl(nfc->regs + NFC_REG_CTL) |
 			       NFC_DMA_TYPE_NORMAL, nfc->regs + NFC_REG_CTL);
-
-	} else {
-		dev_warn(dev, "failed to request rxtx DMA channel\n");
 	}
 
 	platform_set_drvdata(pdev, nfc);