net: mhi: Add protocol support

MHI can transport different protocols, some are handled at upper level,
like IP and QMAP(rmnet/netlink), but others will need to be inside MHI
net driver, like mbim. This change adds support for protocol rx and
tx_fixup callbacks registration, that can be used to encode/decode the
targeted protocol.

Signed-off-by: Loic Poulain <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/mhi_net.c

···
 	struct net_device *ndev;
 	struct sk_buff *skbagg_head;
 	struct sk_buff *skbagg_tail;
+	const struct mhi_net_proto *proto;
+	void *proto_data;
 	struct delayed_work rx_refill;
 	struct mhi_net_stats stats;
 	u32 rx_queue_sz;
+};
+
+struct mhi_net_proto {
+	int (*init)(struct mhi_net_dev *mhi_netdev);
+	struct sk_buff * (*tx_fixup)(struct mhi_net_dev *mhi_netdev, struct sk_buff *skb);
+	void (*rx)(struct mhi_net_dev *mhi_netdev, struct sk_buff *skb);
+};
+
+struct mhi_device_info {
+	const char *netname;
+	const struct mhi_net_proto *proto;
 };
 
 static int mhi_ndo_open(struct net_device *ndev)
···
 static int mhi_ndo_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
 	struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);
+	const struct mhi_net_proto *proto = mhi_netdev->proto;
 	struct mhi_device *mdev = mhi_netdev->mdev;
 	int err;
+
+	if (proto && proto->tx_fixup) {
+		skb = proto->tx_fixup(mhi_netdev, skb);
+		if (unlikely(!skb))
+			goto exit_drop;
+	}
 
 	err = mhi_queue_skb(mdev, DMA_TO_DEVICE, skb, skb->len, MHI_EOT);
 	if (unlikely(err)) {
 		net_err_ratelimited("%s: Failed to queue TX buf (%d)\n",
 				    ndev->name, err);
-
-		u64_stats_update_begin(&mhi_netdev->stats.tx_syncp);
-		u64_stats_inc(&mhi_netdev->stats.tx_dropped);
-		u64_stats_update_end(&mhi_netdev->stats.tx_syncp);
-
-		/* drop the packet */
 		dev_kfree_skb_any(skb);
+		goto exit_drop;
 	}
 
 	if (mhi_queue_is_full(mdev, DMA_TO_DEVICE))
 		netif_stop_queue(ndev);
+
+	return NETDEV_TX_OK;
+
+exit_drop:
+	u64_stats_update_begin(&mhi_netdev->stats.tx_syncp);
+	u64_stats_inc(&mhi_netdev->stats.tx_dropped);
+	u64_stats_update_end(&mhi_netdev->stats.tx_syncp);
 
 	return NETDEV_TX_OK;
 }
···
 				struct mhi_result *mhi_res)
 {
 	struct mhi_net_dev *mhi_netdev = dev_get_drvdata(&mhi_dev->dev);
+	const struct mhi_net_proto *proto = mhi_netdev->proto;
 	struct sk_buff *skb = mhi_res->buf_addr;
 	int free_desc_count;
 
···
 			break;
 		}
 
-		netif_rx(skb);
+		if (proto && proto->rx)
+			proto->rx(mhi_netdev, skb);
+		else
+			netif_rx(skb);
 	}
 
 	/* Refill if RX buffers queue becomes low */
···
 static int mhi_net_probe(struct mhi_device *mhi_dev,
 			 const struct mhi_device_id *id)
 {
-	const char *netname = (char *)id->driver_data;
+	const struct mhi_device_info *info = (struct mhi_device_info *)id->driver_data;
 	struct device *dev = &mhi_dev->dev;
 	struct mhi_net_dev *mhi_netdev;
 	struct net_device *ndev;
 	int err;
 
-	ndev = alloc_netdev(sizeof(*mhi_netdev), netname, NET_NAME_PREDICTABLE,
-			    mhi_net_setup);
+	ndev = alloc_netdev(sizeof(*mhi_netdev), info->netname,
+			    NET_NAME_PREDICTABLE, mhi_net_setup);
 	if (!ndev)
 		return -ENOMEM;
 
···
 	mhi_netdev->ndev = ndev;
 	mhi_netdev->mdev = mhi_dev;
 	mhi_netdev->skbagg_head = NULL;
+	mhi_netdev->proto = info->proto;
 	SET_NETDEV_DEV(ndev, &mhi_dev->dev);
 	SET_NETDEV_DEVTYPE(ndev, &wwan_type);
 
···
 	if (err)
 		goto out_err;
 
+	if (mhi_netdev->proto) {
+		err = mhi_netdev->proto->init(mhi_netdev);
+		if (err)
+			goto out_err_proto;
+	}
+
 	return 0;
 
+out_err_proto:
+	unregister_netdev(ndev);
 out_err:
 	free_netdev(ndev);
 	return err;
···
 	free_netdev(mhi_netdev->ndev);
 }
 
+static const struct mhi_device_info mhi_hwip0 = {
+	.netname = "mhi_hwip%d",
+};
+
+static const struct mhi_device_info mhi_swip0 = {
+	.netname = "mhi_swip%d",
+};
+
 static const struct mhi_device_id mhi_net_id_table[] = {
-	{ .chan = "IP_HW0", .driver_data = (kernel_ulong_t)"mhi_hwip%d" },
-	{ .chan = "IP_SW0", .driver_data = (kernel_ulong_t)"mhi_swip%d" },
+	/* Hardware accelerated data PATH (to modem IPA), protocol agnostic */
+	{ .chan = "IP_HW0", .driver_data = (kernel_ulong_t)&mhi_hwip0 },
+	/* Software data PATH (to modem CPU) */
+	{ .chan = "IP_SW0", .driver_data = (kernel_ulong_t)&mhi_swip0 },
 	{}
 };
 MODULE_DEVICE_TABLE(mhi, mhi_net_id_table);