net: stmmac: enable tx queue 0 for gmac4 IPs synthesized with multiple TX queues

The dwmac4 IP can synthesized with 1-8 number of tx queues.
On an IP synthesized with DWC_EQOS_NUM_TXQ > 1, all txqueues are disabled
by default. For these IPs, the bitfield TXQEN is R/W.

Always enable tx queue 0. The write will have no effect on IPs synthesized
with DWC_EQOS_NUM_TXQ == 1.

The driver does still not utilize more than one tx queue in the IP.
Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac4.h

@@ -155,8 +155,11 @@ enum power_event {
 #define MTL_CHAN_RX_DEBUG(x)		(MTL_CHANX_BASE_ADDR(x) + 0x38)
 
 #define MTL_OP_MODE_RSF			BIT(5)
+#define MTL_OP_MODE_TXQEN		BIT(3)
 #define MTL_OP_MODE_TSF			BIT(1)
 
+#define MTL_OP_MODE_TQS_MASK		GENMASK(24, 16)
+
 #define MTL_OP_MODE_TTC_MASK		0x70
 #define MTL_OP_MODE_TTC_SHIFT		4
 

drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c

@@ -213,7 +213,17 @@ static void dwmac4_dma_chan_op_mode(void __iomem *ioaddr, int txmode,
 		else
 			mtl_tx_op |= MTL_OP_MODE_TTC_512;
 	}
-
+	/* For an IP with DWC_EQOS_NUM_TXQ == 1, the fields TXQEN and TQS are RO
+	 * with reset values: TXQEN on, TQS == DWC_EQOS_TXFIFO_SIZE.
+	 * For an IP with DWC_EQOS_NUM_TXQ > 1, the fields TXQEN and TQS are R/W
+	 * with reset values: TXQEN off, TQS 256 bytes.
+	 *
+	 * Write the bits in both cases, since it will have no effect when RO.
+	 * For DWC_EQOS_NUM_TXQ > 1, the top bits in MTL_OP_MODE_TQS_MASK might
+	 * be RO, however, writing the whole TQS field will result in a value
+	 * equal to DWC_EQOS_TXFIFO_SIZE, just like for DWC_EQOS_NUM_TXQ == 1.
+	 */
+	mtl_tx_op |= MTL_OP_MODE_TXQEN | MTL_OP_MODE_TQS_MASK;
 	writel(mtl_tx_op, ioaddr +  MTL_CHAN_TX_OP_MODE(channel));
 
 	mtl_rx_op = readl(ioaddr + MTL_CHAN_RX_OP_MODE(channel));