mmc: dw_mmc: Add check for IDMAC configuration

In the current dwmmc driver there is support for selecting IDMAC from
the menu config option. If the support for IDMAC is enabled in the menu
config and the hardware configuration register's DMA_INTERFACE field is
0, the driver will still try to do the DMA initialization.

The dw_mci_idmac_init function currently implemented returns only success
indicating that the DMA initialization is always successful. This patch
adds a check for existence of the DMA IP to allow the DMA initialization.
Signed-off-by: Girish K S <girish.shivananjappa@linaro.org>
Acked-by: Will Newton <will.newton@imgtec.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/dw_mmc.c

@@ -405,11 +405,23 @@ static void dw_mci_idmac_start_dma(struct dw_mci *host, unsigned int sg_len)
 static int dw_mci_idmac_init(struct dw_mci *host)
 {
 	struct idmac_desc *p;
-	int i;
+	int i, dma_support;
 
 	/* Number of descriptors in the ring buffer */
 	host->ring_size = PAGE_SIZE / sizeof(struct idmac_desc);
 
+	/* Check if Hardware Configuration Register has support for DMA */
+	dma_support = (mci_readl(host, HCON) >> 16) & 0x3;
+
+	if (!dma_support || dma_support > 2) {
+		dev_err(&host->dev,
+			"Host Controller does not support IDMA Tx.\n");
+		host->dma_ops = NULL;
+		return -ENODEV;
+	}
+
+	dev_info(&host->dev, "Using internal DMA controller.\n");
+
 	/* Forward link the descriptor list */
 	for (i = 0, p = host->sg_cpu; i < host->ring_size - 1; i++, p++)
 		p->des3 = host->sg_dma + (sizeof(struct idmac_desc) * (i + 1));
@@ -1876,7 +1888,6 @@ static void dw_mci_init_dma(struct dw_mci *host)
 	/* Determine which DMA interface to use */
 #ifdef CONFIG_MMC_DW_IDMAC
 	host->dma_ops = &dw_mci_idmac_ops;
-	dev_info(&host->dev, "Using internal DMA controller.\n");
 #endif
 
 	if (!host->dma_ops)