net: ethernet: mtk_eth_soc: support named IRQs

Add named interrupts and keep index based fallback for existing
devicetrees.

Currently only rx and tx IRQs are defined to be used with mt7988, but
later extended with RSS/LRO support.

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: Simon Horman <horms@kernel.org>
---
v6:
- change irq names from tx/rx to fe1/fe2 because reserved irqs
  are usable and not bound to specific function
- dropped Simons RB because of this
v5:
- fix typo in description
- add comments from previous patch #3 with changes suggested by simon

v2:
- move irqs loading part into own helper function
- reduce indentation
- place mtk_get_irqs helper before the irq_handler (note for simon)

net: mtk_eth_soc: change irq name back to fe1 + fe2

Author: frank-w

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -3336,6 +3336,37 @@ static void mtk_tx_timeout(struct net_device *dev, unsigned int txqueue)
 	schedule_work(&eth->pending_work);
 }
 
+static int mtk_get_irqs(struct platform_device *pdev, struct mtk_eth *eth)
+{
+	int i;
+
+	/* future SoCs beginning with MT7988 should use named IRQs in dts */
+	eth->irq[1] = platform_get_irq_byname(pdev, "fe1");
+	eth->irq[2] = platform_get_irq_byname(pdev, "fe2");
+	if (eth->irq[1] >= 0 && eth->irq[2] >= 0)
+		return 0;
+
+	/* legacy way:
+	 * On MTK_SHARED_INT SoCs (MT7621 + MT7628) the first IRQ is taken
+	 * from devicetree and used for both RX and TX - it is shared.
+	 * On SoCs with non-shared IRQs the first entry is not used,
+	 * the second is for TX, and the third is for RX.
+	 */
+	for (i = 0; i < 3; i++) {
+		if (MTK_HAS_CAPS(eth->soc->caps, MTK_SHARED_INT) && i > 0)
+			eth->irq[i] = eth->irq[0];
+		else
+			eth->irq[i] = platform_get_irq(pdev, i);
+
+		if (eth->irq[i] < 0) {
+			dev_err(&pdev->dev, "no IRQ%d resource found\n", i);
+			return -ENXIO;
+		}
+	}
+
+	return 0;
+}
+
 static irqreturn_t mtk_handle_irq_rx(int irq, void *_eth)
 {
 	struct mtk_eth *eth = _eth;
@@ -5105,17 +5136,10 @@ static int mtk_probe(struct platform_device *pdev)
 		}
 	}
 
-	for (i = 0; i < 3; i++) {
-		if (MTK_HAS_CAPS(eth->soc->caps, MTK_SHARED_INT) && i > 0)
-			eth->irq[i] = eth->irq[0];
-		else
-			eth->irq[i] = platform_get_irq(pdev, i);
-		if (eth->irq[i] < 0) {
-			dev_err(&pdev->dev, "no IRQ%d resource found\n", i);
-			err = -ENXIO;
-			goto err_wed_exit;
-		}
-	}
+	err = mtk_get_irqs(pdev, eth);
+	if (err)
+		goto err_wed_exit;
+
 	for (i = 0; i < ARRAY_SIZE(eth->clks); i++) {
 		eth->clks[i] = devm_clk_get(eth->dev,
 					    mtk_clks_source_name[i]);