Revert "net: stmmac: Specify hardware capability value when FIFO size isn't specified"

This reverts commit 8865d22, which caused breakage for platforms
which are not using xgmac2 or gmac4. Only these two cores have the
capability of providing the FIFO sizes from hardware capability fields
(which are provided in priv->dma_cap.[tr]x_fifo_size.)

All other cores can not, which results in these two fields containing
zero. We also have platforms that do not provide a value in
priv->plat->[tr]x_fifo_size, resulting in these also being zero.

This causes the new tests introduced by the reverted commit to fail,
and produce e.g.:

	stmmaceth f0804000.eth: Can't specify Rx FIFO size

An example of such a platform which fails is QEMU's npcm750-evb.
This uses dwmac1000 which, as noted above, does not have the capability
to provide the FIFO sizes from hardware.

Therefore, revert the commit to maintain compatibility with the way
the driver used to work.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/4e98f967-f636-46fb-9eca-d383b9495b86@roeck-us.net
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Tested-by: Steven Price <steven.price@arm.com>
Fixes: 8865d22 ("net: stmmac: Specify hardware capability value when FIFO size isn't specified")
Link: https://patch.msgid.link/E1tfeyR-003YGJ-Gb@rmk-PC.armlinux.org.uk
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: Russell King (Oracle)

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

@@ -2424,6 +2424,11 @@ static void stmmac_dma_operation_mode(struct stmmac_priv *priv)
 	u32 chan = 0;
 	u8 qmode = 0;
 
+	if (rxfifosz == 0)
+		rxfifosz = priv->dma_cap.rx_fifo_size;
+	if (txfifosz == 0)
+		txfifosz = priv->dma_cap.tx_fifo_size;
+
 	/* Split up the shared Tx/Rx FIFO memory on DW QoS Eth and DW XGMAC */
 	if (priv->plat->has_gmac4 || priv->plat->has_xgmac) {
 		rxfifosz /= rx_channels_count;
@@ -2892,6 +2897,11 @@ static void stmmac_set_dma_operation_mode(struct stmmac_priv *priv, u32 txmode,
 	int rxfifosz = priv->plat->rx_fifo_size;
 	int txfifosz = priv->plat->tx_fifo_size;
 
+	if (rxfifosz == 0)
+		rxfifosz = priv->dma_cap.rx_fifo_size;
+	if (txfifosz == 0)
+		txfifosz = priv->dma_cap.tx_fifo_size;
+
 	/* Adjust for real per queue fifo size */
 	rxfifosz /= rx_channels_count;
 	txfifosz /= tx_channels_count;
@@ -5868,6 +5878,9 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 	const int mtu = new_mtu;
 	int ret;
 
+	if (txfifosz == 0)
+		txfifosz = priv->dma_cap.tx_fifo_size;
+
 	txfifosz /= priv->plat->tx_queues_to_use;
 
 	if (stmmac_xdp_is_enabled(priv) && new_mtu > ETH_DATA_LEN) {
@@ -7219,29 +7232,15 @@ static int stmmac_hw_init(struct stmmac_priv *priv)
 		priv->plat->tx_queues_to_use = priv->dma_cap.number_tx_queues;
 	}
 
-	if (!priv->plat->rx_fifo_size) {
-		if (priv->dma_cap.rx_fifo_size) {
-			priv->plat->rx_fifo_size = priv->dma_cap.rx_fifo_size;
-		} else {
-			dev_err(priv->device, "Can't specify Rx FIFO size\n");
-			return -ENODEV;
-		}
-	} else if (priv->dma_cap.rx_fifo_size &&
-		   priv->plat->rx_fifo_size > priv->dma_cap.rx_fifo_size) {
+	if (priv->dma_cap.rx_fifo_size &&
+	    priv->plat->rx_fifo_size > priv->dma_cap.rx_fifo_size) {
 		dev_warn(priv->device,
 			 "Rx FIFO size (%u) exceeds dma capability\n",
 			 priv->plat->rx_fifo_size);
 		priv->plat->rx_fifo_size = priv->dma_cap.rx_fifo_size;
 	}
-	if (!priv->plat->tx_fifo_size) {
-		if (priv->dma_cap.tx_fifo_size) {
-			priv->plat->tx_fifo_size = priv->dma_cap.tx_fifo_size;
-		} else {
-			dev_err(priv->device, "Can't specify Tx FIFO size\n");
-			return -ENODEV;
-		}
-	} else if (priv->dma_cap.tx_fifo_size &&
-		   priv->plat->tx_fifo_size > priv->dma_cap.tx_fifo_size) {
+	if (priv->dma_cap.tx_fifo_size &&
+	    priv->plat->tx_fifo_size > priv->dma_cap.tx_fifo_size) {
 		dev_warn(priv->device,
 			 "Tx FIFO size (%u) exceeds dma capability\n",
 			 priv->plat->tx_fifo_size);