chelsio: cxgb: Use dma_set_mask_and_coherent() and simplify code

Use dma_set_mask_and_coherent() instead of unrolling it with some
dma_set_mask()+dma_set_coherent_mask().

Moreover, as stated in [1], dma_set_mask() with a 64-bit mask will never
fail if dev->dma_mask is non-NULL.
So, if it fails, the 32 bits case will also fail for the same reason.

That said, 'pci_using_dac' can only be 1 after a successful
dma_set_mask_and_coherent().

Simplify code and remove some dead code accordingly.

[1]: https://lkml.org/lkml/2021/6/7/398

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb/cxgb2.c

@@ -944,11 +944,11 @@ static const struct net_device_ops cxgb_netdev_ops = {
 
 static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 {
-	int i, err, pci_using_dac = 0;
 	unsigned long mmio_start, mmio_len;
 	const struct board_info *bi;
 	struct adapter *adapter = NULL;
 	struct port_info *pi;
+	int i, err;
 
 	err = pci_enable_device(pdev);
 	if (err)
@@ -961,17 +961,8 @@ static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto out_disable_pdev;
 	}
 
-	if (!dma_set_mask(&pdev->dev, DMA_BIT_MASK(64))) {
-		pci_using_dac = 1;
-
-		if (dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(64))) {
-			pr_err("%s: unable to obtain 64-bit DMA for coherent allocations\n",
-			       pci_name(pdev));
-			err = -ENODEV;
-			goto out_disable_pdev;
-		}
-
-	} else if ((err = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32))) != 0) {
+	err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
+	if (err) {
 		pr_err("%s: no usable DMA configuration\n", pci_name(pdev));
 		goto out_disable_pdev;
 	}
@@ -1043,10 +1034,8 @@ static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 		netdev->hw_features |= NETIF_F_SG | NETIF_F_IP_CSUM |
 			NETIF_F_RXCSUM;
 		netdev->features |= NETIF_F_SG | NETIF_F_IP_CSUM |
-			NETIF_F_RXCSUM | NETIF_F_LLTX;
+			NETIF_F_RXCSUM | NETIF_F_LLTX | NETIF_F_HIGHDMA;
 
-		if (pci_using_dac)
-			netdev->features |= NETIF_F_HIGHDMA;
 		if (vlan_tso_capable(adapter)) {
 			netdev->features |=
 				NETIF_F_HW_VLAN_CTAG_TX |