net: ethernet: mtk_eth_soc: use iopoll.h macro for DMA init

Replace a tight busy-wait loop without a pause with a standard
readx_poll_timeout_atomic routine with a 5 us poll period.

Tested by booting a MT7621 device to ensure the driver initializes
properly.
Signed-off-by: NIlya Lipnitskiy <ilya.lipnitskiy@gmail.com>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -2033,25 +2033,22 @@ static int mtk_set_features(struct net_device *dev, netdev_features_t features)
 /* wait for DMA to finish whatever it is doing before we start using it again */
 static int mtk_dma_busy_wait(struct mtk_eth *eth)
 {
-	unsigned long t_start = jiffies;
+	unsigned int reg;
+	int ret;
+	u32 val;
 
-	while (1) {
-		if (MTK_HAS_CAPS(eth->soc->caps, MTK_QDMA)) {
-			if (!(mtk_r32(eth, MTK_QDMA_GLO_CFG) &
-			      (MTK_RX_DMA_BUSY | MTK_TX_DMA_BUSY)))
-				return 0;
-		} else {
-			if (!(mtk_r32(eth, MTK_PDMA_GLO_CFG) &
-			      (MTK_RX_DMA_BUSY | MTK_TX_DMA_BUSY)))
-				return 0;
-		}
+	if (MTK_HAS_CAPS(eth->soc->caps, MTK_QDMA))
+		reg = MTK_QDMA_GLO_CFG;
+	else
+		reg = MTK_PDMA_GLO_CFG;
 
-		if (time_after(jiffies, t_start + MTK_DMA_BUSY_TIMEOUT))
-			break;
-	}
+	ret = readx_poll_timeout_atomic(__raw_readl, eth->base + reg, val,
+					!(val & (MTK_RX_DMA_BUSY | MTK_TX_DMA_BUSY)),
+					5, MTK_DMA_BUSY_TIMEOUT_US);
+	if (ret)
+		dev_err(eth->dev, "DMA init timeout\n");
 
-	dev_err(eth->dev, "DMA init timeout\n");
-	return -1;
+	return ret;
 }
 
 static int mtk_dma_init(struct mtk_eth *eth)

drivers/net/ethernet/mediatek/mtk_eth_soc.h

@@ -214,7 +214,7 @@
 #define MTK_TX_DMA_BUSY		BIT(1)
 #define MTK_RX_DMA_EN		BIT(2)
 #define MTK_TX_DMA_EN		BIT(0)
-#define MTK_DMA_BUSY_TIMEOUT	HZ
+#define MTK_DMA_BUSY_TIMEOUT_US	1000000
 
 /* QDMA Reset Index Register */
 #define MTK_QDMA_RST_IDX	0x1A08