net: configure DWMAC DMA by default AXI burst length

Board can define its own AXI burst length to improve DWMAC DMA performance.

v2-changes:
- Avoid write burst len register when the Macro is not defined.

v3-changes:
- Add axi_bus register member to struct eth_dma_regs.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

drivers/net/designware.c

@@ -258,6 +258,10 @@ static int dw_eth_init(struct eth_device *dev, bd_t *bis)
 
 	writel(readl(&dma_p->opmode) | RXSTART | TXSTART, &dma_p->opmode);
 
+#ifdef CONFIG_DW_AXI_BURST_LEN
+	writel((CONFIG_DW_AXI_BURST_LEN & 0x1FF >> 1), &dma_p->axibus);
+#endif
+
 	/* Start up the PHY */
 	if (phy_startup(priv->phydev)) {
 		printf("Could not initialize PHY %s\n",

drivers/net/designware.h

@@ -68,7 +68,9 @@ struct eth_dma_regs {
 	u32 status;		/* 0x14 */
 	u32 opmode;		/* 0x18 */
 	u32 intenable;		/* 0x1c */
-	u8 reserved[40];
+	u32 reserved1[2];
+	u32 axibus;		/* 0x28 */
+	u32 reserved2[7];
 	u32 currhosttxdesc;	/* 0x48 */
 	u32 currhostrxdesc;	/* 0x4c */
 	u32 currhosttxbuffaddr;	/* 0x50 */