net: mhi: Add mbim proto

MBIM has initially been specified by USB-IF for transporting data (IP)
between a modem and a host over USB. However some modern modems also
support MBIM over PCIe (via MHI). In the same way as QMAP(rmnet), it
allows to aggregate IP packets and to perform context multiplexing.

This change adds minimal MBIM data transport support to MHI, allowing
to support MBIM only modems. MBIM being based on USB NCM, it reuses
and copy some helpers/functions from the USB stack (cdc-ncm, cdc-mbim).

Note that is a subset of the CDC-MBIM specification, supporting only
transport of network data (IP), there is no support for DSS. Moreover
the multi-session (for multi-pdn) is not supported in this initial
version, but will be added latter, and aligned with the cdc-mbim
solution (VLAN tags).

This code has been inspired from the mhi_mbim downstream implementation
(Carl Yin <carl.yin@quectel.com>).
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/mhi/Makefile

 obj-$(CONFIG_MHI_NET) += mhi_net.o
 
-mhi_net-y := net.o
+mhi_net-y := net.o proto_mbim.o

drivers/net/mhi/mhi.h

@@ -28,6 +28,7 @@ struct mhi_net_dev {
 	struct delayed_work rx_refill;
 	struct mhi_net_stats stats;
 	u32 rx_queue_sz;
+	int msg_enable;
 };
 
 struct mhi_net_proto {
@@ -35,3 +36,5 @@ struct mhi_net_proto {
 	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);
 };
+
+extern const struct mhi_net_proto proto_mbim;

drivers/net/mhi/net.c

@@ -373,11 +373,18 @@ static const struct mhi_device_info mhi_swip0 = {
 	.netname = "mhi_swip%d",
 };
 
+static const struct mhi_device_info mhi_hwip0_mbim = {
+	.netname = "mhi_mbim%d",
+	.proto = &proto_mbim,
+};
+
 static const struct mhi_device_id mhi_net_id_table[] = {
 	/* 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 },
+	/* Hardware accelerated data PATH (to modem IPA), MBIM protocol */
+	{ .chan = "IP_HW0_MBIM", .driver_data = (kernel_ulong_t)&mhi_hwip0_mbim },
 	{}
 };
 MODULE_DEVICE_TABLE(mhi, mhi_net_id_table);

drivers/net/mhi/proto_mbim.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+/* MHI Network driver - Network over MHI bus
+ *
+ * Copyright (C) 2021 Linaro Ltd <loic.poulain@linaro.org>
+ *
+ * This driver copy some code from cdc_ncm, which is:
+ * Copyright (C) ST-Ericsson 2010-2012
+ * and cdc_mbim, which is:
+ * Copyright (c) 2012  Smith Micro Software, Inc.
+ * Copyright (c) 2012  Bjørn Mork <bjorn@mork.no>
+ *
+ */
+
+#include <linux/ethtool.h>
+#include <linux/if_vlan.h>
+#include <linux/ip.h>
+#include <linux/mii.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/usb.h>
+#include <linux/usb/cdc.h>
+#include <linux/usb/usbnet.h>
+#include <linux/usb/cdc_ncm.h>
+
+#include "mhi.h"
+
+#define MBIM_NDP16_SIGN_MASK 0x00ffffff
+
+struct mbim_context {
+	u16 rx_seq;
+	u16 tx_seq;
+};
+
+static void __mbim_length_errors_inc(struct mhi_net_dev *dev)
+{
+	u64_stats_update_begin(&dev->stats.rx_syncp);
+	u64_stats_inc(&dev->stats.rx_length_errors);
+	u64_stats_update_end(&dev->stats.rx_syncp);
+}
+
+static void __mbim_errors_inc(struct mhi_net_dev *dev)
+{
+	u64_stats_update_begin(&dev->stats.rx_syncp);
+	u64_stats_inc(&dev->stats.rx_errors);
+	u64_stats_update_end(&dev->stats.rx_syncp);
+}
+
+static int mbim_rx_verify_nth16(struct sk_buff *skb)
+{
+	struct mhi_net_dev *dev = netdev_priv(skb->dev);
+	struct mbim_context *ctx = dev->proto_data;
+	struct usb_cdc_ncm_nth16 *nth16;
+	int len;
+
+	if (skb->len < sizeof(struct usb_cdc_ncm_nth16) +
+			sizeof(struct usb_cdc_ncm_ndp16)) {
+		netif_dbg(dev, rx_err, dev->ndev, "frame too short\n");
+		__mbim_length_errors_inc(dev);
+		return -EINVAL;
+	}
+
+	nth16 = (struct usb_cdc_ncm_nth16 *)skb->data;
+
+	if (nth16->dwSignature != cpu_to_le32(USB_CDC_NCM_NTH16_SIGN)) {
+		netif_dbg(dev, rx_err, dev->ndev,
+			  "invalid NTH16 signature <%#010x>\n",
+			  le32_to_cpu(nth16->dwSignature));
+		__mbim_errors_inc(dev);
+		return -EINVAL;
+	}
+
+	/* No limit on the block length, except the size of the data pkt */
+	len = le16_to_cpu(nth16->wBlockLength);
+	if (len > skb->len) {
+		netif_dbg(dev, rx_err, dev->ndev,
+			  "NTB does not fit into the skb %u/%u\n", len,
+			  skb->len);
+		__mbim_length_errors_inc(dev);
+		return -EINVAL;
+	}
+
+	if (ctx->rx_seq + 1 != le16_to_cpu(nth16->wSequence) &&
+	    (ctx->rx_seq || le16_to_cpu(nth16->wSequence)) &&
+	    !(ctx->rx_seq == 0xffff && !le16_to_cpu(nth16->wSequence))) {
+		netif_dbg(dev, rx_err, dev->ndev,
+			  "sequence number glitch prev=%d curr=%d\n",
+			  ctx->rx_seq, le16_to_cpu(nth16->wSequence));
+	}
+	ctx->rx_seq = le16_to_cpu(nth16->wSequence);
+
+	return le16_to_cpu(nth16->wNdpIndex);
+}
+
+static int mbim_rx_verify_ndp16(struct sk_buff *skb, int ndpoffset)
+{
+	struct mhi_net_dev *dev = netdev_priv(skb->dev);
+	struct usb_cdc_ncm_ndp16 *ndp16;
+	int ret;
+
+	if (ndpoffset + sizeof(struct usb_cdc_ncm_ndp16) > skb->len) {
+		netif_dbg(dev, rx_err, dev->ndev, "invalid NDP offset  <%u>\n",
+			  ndpoffset);
+		return -EINVAL;
+	}
+
+	ndp16 = (struct usb_cdc_ncm_ndp16 *)(skb->data + ndpoffset);
+
+	if (le16_to_cpu(ndp16->wLength) < USB_CDC_NCM_NDP16_LENGTH_MIN) {
+		netif_dbg(dev, rx_err, dev->ndev, "invalid DPT16 length <%u>\n",
+			  le16_to_cpu(ndp16->wLength));
+		return -EINVAL;
+	}
+
+	ret = ((le16_to_cpu(ndp16->wLength) - sizeof(struct usb_cdc_ncm_ndp16))
+			/ sizeof(struct usb_cdc_ncm_dpe16));
+	ret--; /* Last entry is always a NULL terminator */
+
+	if (sizeof(struct usb_cdc_ncm_ndp16) +
+	     ret * sizeof(struct usb_cdc_ncm_dpe16) > skb->len) {
+		netif_dbg(dev, rx_err, dev->ndev,
+			  "Invalid nframes = %d\n", ret);
+		return -EINVAL;
+	}
+
+	return ret;
+}
+
+static void mbim_rx(struct mhi_net_dev *mhi_netdev, struct sk_buff *skb)
+{
+	struct net_device *ndev = mhi_netdev->ndev;
+	int ndpoffset;
+
+	if (skb_linearize(skb))
+		goto error;
+
+	/* Check NTB header and retrieve first NDP offset */
+	ndpoffset = mbim_rx_verify_nth16(skb);
+	if (ndpoffset < 0) {
+		net_err_ratelimited("%s: Incorrect NTB header\n", ndev->name);
+		goto error;
+	}
+
+	/* Process each NDP */
+	while (1) {
+		struct usb_cdc_ncm_ndp16 *ndp16;
+		struct usb_cdc_ncm_dpe16 *dpe16;
+		int nframes, n;
+
+		/* Check NDP header and retrieve number of datagrams */
+		nframes = mbim_rx_verify_ndp16(skb, ndpoffset);
+		if (nframes < 0) {
+			net_err_ratelimited("%s: Incorrect NDP16\n", ndev->name);
+			__mbim_length_errors_inc(mhi_netdev);
+			goto error;
+		}
+
+		 /* Only IP data type supported, no DSS in MHI context */
+		ndp16 = (struct usb_cdc_ncm_ndp16 *)(skb->data + ndpoffset);
+		if ((ndp16->dwSignature & cpu_to_le32(MBIM_NDP16_SIGN_MASK))
+				!= cpu_to_le32(USB_CDC_MBIM_NDP16_IPS_SIGN)) {
+			net_err_ratelimited("%s: Unsupported NDP type\n", ndev->name);
+			__mbim_errors_inc(mhi_netdev);
+			goto next_ndp;
+		}
+
+		/* Only primary IP session 0 (0x00) supported for now */
+		if (ndp16->dwSignature & ~cpu_to_le32(MBIM_NDP16_SIGN_MASK)) {
+			net_err_ratelimited("%s: bad packet session\n", ndev->name);
+			__mbim_errors_inc(mhi_netdev);
+			goto next_ndp;
+		}
+
+		/* de-aggregate and deliver IP packets */
+		dpe16 = ndp16->dpe16;
+		for (n = 0; n < nframes; n++, dpe16++) {
+			u16 dgram_offset = le16_to_cpu(dpe16->wDatagramIndex);
+			u16 dgram_len = le16_to_cpu(dpe16->wDatagramLength);
+			struct sk_buff *skbn;
+
+			if (!dgram_offset || !dgram_len)
+				break; /* null terminator */
+
+			skbn = netdev_alloc_skb(ndev, dgram_len);
+			if (!skbn)
+				continue;
+
+			skb_put(skbn, dgram_len);
+			memcpy(skbn->data, skb->data + dgram_offset, dgram_len);
+
+			switch (skbn->data[0] & 0xf0) {
+			case 0x40:
+				skbn->protocol = htons(ETH_P_IP);
+				break;
+			case 0x60:
+				skbn->protocol = htons(ETH_P_IPV6);
+				break;
+			default:
+				net_err_ratelimited("%s: unknown protocol\n",
+						    ndev->name);
+				__mbim_errors_inc(mhi_netdev);
+				dev_kfree_skb_any(skbn);
+				continue;
+			}
+
+			netif_rx(skbn);
+		}
+next_ndp:
+		/* Other NDP to process? */
+		ndpoffset = (int)le16_to_cpu(ndp16->wNextNdpIndex);
+		if (!ndpoffset)
+			break;
+	}
+
+	/* free skb */
+	dev_consume_skb_any(skb);
+	return;
+error:
+	dev_kfree_skb_any(skb);
+}
+
+struct mbim_tx_hdr {
+	struct usb_cdc_ncm_nth16 nth16;
+	struct usb_cdc_ncm_ndp16 ndp16;
+	struct usb_cdc_ncm_dpe16 dpe16[2];
+} __packed;
+
+static struct sk_buff *mbim_tx_fixup(struct mhi_net_dev *mhi_netdev,
+				     struct sk_buff *skb)
+{
+	struct mbim_context *ctx = mhi_netdev->proto_data;
+	unsigned int dgram_size = skb->len;
+	struct usb_cdc_ncm_nth16 *nth16;
+	struct usb_cdc_ncm_ndp16 *ndp16;
+	struct mbim_tx_hdr *mbim_hdr;
+
+	/* For now, this is a partial implementation of CDC MBIM, only one NDP
+	 * is sent, containing the IP packet (no aggregation).
+	 */
+
+	/* Ensure we have enough headroom for crafting MBIM header */
+	if (skb_cow_head(skb, sizeof(struct mbim_tx_hdr))) {
+		dev_kfree_skb_any(skb);
+		return NULL;
+	}
+
+	mbim_hdr = skb_push(skb, sizeof(struct mbim_tx_hdr));
+
+	/* Fill NTB header */
+	nth16 = &mbim_hdr->nth16;
+	nth16->dwSignature = cpu_to_le32(USB_CDC_NCM_NTH16_SIGN);
+	nth16->wHeaderLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16));
+	nth16->wSequence = cpu_to_le16(ctx->tx_seq++);
+	nth16->wBlockLength = cpu_to_le16(skb->len);
+	nth16->wNdpIndex = cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16));
+
+	/* Fill the unique NDP */
+	ndp16 = &mbim_hdr->ndp16;
+	ndp16->dwSignature = cpu_to_le32(USB_CDC_MBIM_NDP16_IPS_SIGN);
+	ndp16->wLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_ndp16)
+					+ sizeof(struct usb_cdc_ncm_dpe16) * 2);
+	ndp16->wNextNdpIndex = 0;
+
+	/* Datagram follows the mbim header */
+	ndp16->dpe16[0].wDatagramIndex = cpu_to_le16(sizeof(struct mbim_tx_hdr));
+	ndp16->dpe16[0].wDatagramLength = cpu_to_le16(dgram_size);
+
+	/* null termination */
+	ndp16->dpe16[1].wDatagramIndex = 0;
+	ndp16->dpe16[1].wDatagramLength = 0;
+
+	return skb;
+}
+
+static int mbim_init(struct mhi_net_dev *mhi_netdev)
+{
+	struct net_device *ndev = mhi_netdev->ndev;
+
+	mhi_netdev->proto_data = devm_kzalloc(&ndev->dev,
+					      sizeof(struct mbim_context),
+					      GFP_KERNEL);
+	if (!mhi_netdev->proto_data)
+		return -ENOMEM;
+
+	ndev->needed_headroom = sizeof(struct mbim_tx_hdr);
+
+	return 0;
+}
+
+const struct mhi_net_proto proto_mbim = {
+	.init = mbim_init,
+	.rx = mbim_rx,
+	.tx_fixup = mbim_tx_fixup,
+};