mmc: dw_mmc: use macro to define ring buffer size

It's very prone to make mistake as we might forget
to replace all PAGE_SIZEs with new values if we try
to modify the ring buffer size for whatever reasons.
Let's use a macro to define it.
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/dw_mmc.c

@@ -61,6 +61,8 @@
 				 SDMMC_IDMAC_INT_FBE | SDMMC_IDMAC_INT_RI | \
 				 SDMMC_IDMAC_INT_TI)
 
+#define DESC_RING_BUF_SZ	PAGE_SIZE
+
 struct idmac_desc_64addr {
 	u32		des0;	/* Control Descriptor */
 
@@ -474,7 +476,8 @@ static int dw_mci_idmac_init(struct dw_mci *host)
 	if (host->dma_64bit_address == 1) {
 		struct idmac_desc_64addr *p;
 		/* Number of descriptors in the ring buffer */
-		host->ring_size = PAGE_SIZE / sizeof(struct idmac_desc_64addr);
+		host->ring_size =
+			DESC_RING_BUF_SZ / sizeof(struct idmac_desc_64addr);
 
 		/* Forward link the descriptor list */
 		for (i = 0, p = host->sg_cpu; i < host->ring_size - 1;
@@ -500,7 +503,8 @@ static int dw_mci_idmac_init(struct dw_mci *host)
 	} else {
 		struct idmac_desc *p;
 		/* Number of descriptors in the ring buffer */
-		host->ring_size = PAGE_SIZE / sizeof(struct idmac_desc);
+		host->ring_size =
+			DESC_RING_BUF_SZ / sizeof(struct idmac_desc);
 
 		/* Forward link the descriptor list */
 		for (i = 0, p = host->sg_cpu;
@@ -609,7 +613,7 @@ static inline int dw_mci_prepare_desc64(struct dw_mci *host,
 err_own_bit:
 	/* restore the descriptor chain as it's polluted */
 	dev_dbg(host->dev, "desciptor is still owned by IDMAC.\n");
-	memset(host->sg_cpu, 0, PAGE_SIZE);
+	memset(host->sg_cpu, 0, DESC_RING_BUF_SZ);
 	dw_mci_idmac_init(host);
 	return -EINVAL;
 }
@@ -685,7 +689,7 @@ static inline int dw_mci_prepare_desc32(struct dw_mci *host,
 err_own_bit:
 	/* restore the descriptor chain as it's polluted */
 	dev_dbg(host->dev, "desciptor is still owned by IDMAC.\n");
-	memset(host->sg_cpu, 0, PAGE_SIZE);
+	memset(host->sg_cpu, 0, DESC_RING_BUF_SZ);
 	dw_mci_idmac_init(host);
 	return -EINVAL;
 }
@@ -2754,7 +2758,8 @@ static void dw_mci_init_dma(struct dw_mci *host)
 		}
 
 		/* Alloc memory for sg translation */
-		host->sg_cpu = dmam_alloc_coherent(host->dev, PAGE_SIZE,
+		host->sg_cpu = dmam_alloc_coherent(host->dev,
+						   DESC_RING_BUF_SZ,
 						   &host->sg_dma, GFP_KERNEL);
 		if (!host->sg_cpu) {
 			dev_err(host->dev,