--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Management Component Transport Protocol (MCTP) - serial transport
+ * binding. This driver is an implementation of the DMTF specificiation
+ * "DSP0253 - Management Component Transport Protocol (MCTP) Serial Transport
+ * Binding", available at:
+ *
+ * https://www.dmtf.org/sites/default/files/standards/documents/DSP0253_1.0.0.pdf
+ *
+ * This driver provides DSP0253-type MCTP-over-serial transport using a Linux
+ * tty device, by setting the N_MCTP line discipline on the tty.
+ *
+ * Copyright (c) 2021 Code Construct
+ */
+
+#include <linux/idr.h>
+#include <linux/if_arp.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/tty.h>
+#include <linux/workqueue.h>
+#include <linux/crc-ccitt.h>
+
+#include <linux/mctp.h>
+#include <net/mctp.h>
+#include <net/pkt_sched.h>
+
+#define MCTP_SERIAL_MTU 68 /* base mtu (64) + mctp header */
+#define MCTP_SERIAL_FRAME_MTU (MCTP_SERIAL_MTU + 6) /* + serial framing */
+
+#define MCTP_SERIAL_VERSION 0x1 /* DSP0253 defines a single version: 1 */
+
+#define BUFSIZE MCTP_SERIAL_FRAME_MTU
+
+#define BYTE_FRAME 0x7e
+#define BYTE_ESC 0x7d
+
+static DEFINE_IDA(mctp_serial_ida);
+
+enum mctp_serial_state {
+ STATE_IDLE,
+ STATE_START,
+ STATE_HEADER,
+ STATE_DATA,
+ STATE_ESCAPE,
+ STATE_TRAILER,
+ STATE_DONE,
+ STATE_ERR,
+};
+
+struct mctp_serial {
+ struct net_device *netdev;
+ struct tty_struct *tty;
+
+ int idx;
+
+ /* protects our rx & tx state machines; held during both paths */
+ spinlock_t lock;
+
+ struct work_struct tx_work;
+ enum mctp_serial_state txstate, rxstate;
+ u16 txfcs, rxfcs, rxfcs_rcvd;
+ unsigned int txlen, rxlen;
+ unsigned int txpos, rxpos;
+ unsigned char txbuf[BUFSIZE],
+ rxbuf[BUFSIZE];
+};
+
+static bool needs_escape(unsigned char c)
+{
+ return c == BYTE_ESC || c == BYTE_FRAME;
+}
+
+static int next_chunk_len(struct mctp_serial *dev)
+{
+ int i;
+
+ /* either we have no bytes to send ... */
+ if (dev->txpos == dev->txlen)
+ return 0;
+
+ /* ... or the next byte to send is an escaped byte; requiring a
+ * single-byte chunk...
+ */
+ if (needs_escape(dev->txbuf[dev->txpos]))
+ return 1;
+
+ /* ... or we have one or more bytes up to the next escape - this chunk
+ * will be those non-escaped bytes, and does not include the escaped
+ * byte.
+ */
+ for (i = 1; i + dev->txpos + 1 < dev->txlen; i++) {
+ if (needs_escape(dev->txbuf[dev->txpos + i + 1]))
+ break;
+ }
+
+ return i;
+}
+
+static int write_chunk(struct mctp_serial *dev, unsigned char *buf, int len)
+{
+ return dev->tty->ops->write(dev->tty, buf, len);
+}
+
+static void mctp_serial_tx_work(struct work_struct *work)
+{
+ struct mctp_serial *dev = container_of(work, struct mctp_serial,
+ tx_work);
+ unsigned char c, buf[3];
+ unsigned long flags;
+ int len, txlen;
+
+ spin_lock_irqsave(&dev->lock, flags);
+
+ /* txstate represents the next thing to send */
+ switch (dev->txstate) {
+ case STATE_START:
+ dev->txpos = 0;
+ fallthrough;
+ case STATE_HEADER:
+ buf[0] = BYTE_FRAME;
+ buf[1] = MCTP_SERIAL_VERSION;
+ buf[2] = dev->txlen;
+
+ if (!dev->txpos)
+ dev->txfcs = crc_ccitt(0, buf + 1, 2);
+
+ txlen = write_chunk(dev, buf + dev->txpos, 3 - dev->txpos);
+ if (txlen <= 0) {
+ dev->txstate = STATE_ERR;
+ } else {
+ dev->txpos += txlen;
+ if (dev->txpos == 3) {
+ dev->txstate = STATE_DATA;
+ dev->txpos = 0;
+ }
+ }
+ break;
+
+ case STATE_ESCAPE:
+ buf[0] = dev->txbuf[dev->txpos] & ~0x20;
+ txlen = write_chunk(dev, buf, 1);
+ if (txlen <= 0) {
+ dev->txstate = STATE_ERR;
+ } else {
+ dev->txpos += txlen;
+ if (dev->txpos == dev->txlen) {
+ dev->txstate = STATE_TRAILER;
+ dev->txpos = 0;
+ }
+ }
+
+ break;
+
+ case STATE_DATA:
+ len = next_chunk_len(dev);
+ if (len) {
+ c = dev->txbuf[dev->txpos];
+ if (len == 1 && needs_escape(c)) {
+ buf[0] = BYTE_ESC;
+ buf[1] = c & ~0x20;
+ dev->txfcs = crc_ccitt_byte(dev->txfcs, c);
+ txlen = write_chunk(dev, buf, 2);
+ if (txlen == 2)
+ dev->txpos++;
+ else if (txlen == 1)
+ dev->txstate = STATE_ESCAPE;
+ else
+ dev->txstate = STATE_ERR;
+ } else {
+ txlen = write_chunk(dev,
+ dev->txbuf + dev->txpos,
+ len);
+ if (txlen <= 0) {
+ dev->txstate = STATE_ERR;
+ } else {
+ dev->txfcs = crc_ccitt(dev->txfcs,
+ dev->txbuf +
+ dev->txpos,
+ txlen);
+ dev->txpos += txlen;
+ }
+ }
+ if (dev->txstate == STATE_DATA &&
+ dev->txpos == dev->txlen) {
+ dev->txstate = STATE_TRAILER;
+ dev->txpos = 0;
+ }
+ break;
+ }
+ dev->txstate = STATE_TRAILER;
+ dev->txpos = 0;
+ fallthrough;
+
+ case STATE_TRAILER:
+ buf[0] = dev->txfcs >> 8;
+ buf[1] = dev->txfcs & 0xff;
+ buf[2] = BYTE_FRAME;
+ txlen = write_chunk(dev, buf + dev->txpos, 3 - dev->txpos);
+ if (txlen <= 0) {
+ dev->txstate = STATE_ERR;
+ } else {
+ dev->txpos += txlen;
+ if (dev->txpos == 3) {
+ dev->txstate = STATE_DONE;
+ dev->txpos = 0;
+ }
+ }
+ break;
+ default:
+ netdev_err_once(dev->netdev, "invalid tx state %d\n",
+ dev->txstate);
+ }
+
+ if (dev->txstate == STATE_DONE) {
+ dev->netdev->stats.tx_packets++;
+ dev->netdev->stats.tx_bytes += dev->txlen;
+ dev->txlen = 0;
+ dev->txpos = 0;
+ clear_bit(TTY_DO_WRITE_WAKEUP, &dev->tty->flags);
+ dev->txstate = STATE_IDLE;
+ spin_unlock_irqrestore(&dev->lock, flags);
+
+ netif_wake_queue(dev->netdev);
+ } else {
+ spin_unlock_irqrestore(&dev->lock, flags);
+ }
+}
+
+static netdev_tx_t mctp_serial_tx(struct sk_buff *skb, struct net_device *ndev)
+{
+ struct mctp_serial *dev = netdev_priv(ndev);
+ unsigned long flags;
+
+ WARN_ON(dev->txstate != STATE_IDLE);
+
+ if (skb->len > MCTP_SERIAL_MTU) {
+ dev->netdev->stats.tx_dropped++;
+ goto out;
+ }
+
+ spin_lock_irqsave(&dev->lock, flags);
+ netif_stop_queue(dev->netdev);
+ skb_copy_bits(skb, 0, dev->txbuf, skb->len);
+ dev->txpos = 0;
+ dev->txlen = skb->len;
+ dev->txstate = STATE_START;
+ spin_unlock_irqrestore(&dev->lock, flags);
+
+ set_bit(TTY_DO_WRITE_WAKEUP, &dev->tty->flags);
+ schedule_work(&dev->tx_work);
+
+out:
+ kfree_skb(skb);
+ return NETDEV_TX_OK;
+}
+
+static void mctp_serial_tty_write_wakeup(struct tty_struct *tty)
+{
+ struct mctp_serial *dev = tty->disc_data;
+
+ schedule_work(&dev->tx_work);
+}
+
+static void mctp_serial_rx(struct mctp_serial *dev)
+{
+ struct mctp_skb_cb *cb;
+ struct sk_buff *skb;
+
+ if (dev->rxfcs != dev->rxfcs_rcvd) {
+ dev->netdev->stats.rx_dropped++;
+ dev->netdev->stats.rx_crc_errors++;
+ return;
+ }
+
+ skb = netdev_alloc_skb(dev->netdev, dev->rxlen);
+ if (!skb) {
+ dev->netdev->stats.rx_dropped++;
+ return;
+ }
+
+ skb->protocol = htons(ETH_P_MCTP);
+ skb_put_data(skb, dev->rxbuf, dev->rxlen);
+ skb_reset_network_header(skb);
+
+ cb = __mctp_cb(skb);
+ cb->halen = 0;
+
+ netif_rx_ni(skb);
+ dev->netdev->stats.rx_packets++;
+ dev->netdev->stats.rx_bytes += dev->rxlen;
+}
+
+static void mctp_serial_push_header(struct mctp_serial *dev, unsigned char c)
+{
+ switch (dev->rxpos) {
+ case 0:
+ if (c == BYTE_FRAME)
+ dev->rxpos++;
+ else
+ dev->rxstate = STATE_ERR;
+ break;
+ case 1:
+ if (c == MCTP_SERIAL_VERSION) {
+ dev->rxpos++;
+ dev->rxfcs = crc_ccitt_byte(0, c);
+ } else {
+ dev->rxstate = STATE_ERR;
+ }
+ break;
+ case 2:
+ if (c > MCTP_SERIAL_FRAME_MTU) {
+ dev->rxstate = STATE_ERR;
+ } else {
+ dev->rxlen = c;
+ dev->rxpos = 0;
+ dev->rxstate = STATE_DATA;
+ dev->rxfcs = crc_ccitt_byte(dev->rxfcs, c);
+ }
+ break;
+ }
+}
+
+static void mctp_serial_push_trailer(struct mctp_serial *dev, unsigned char c)
+{
+ switch (dev->rxpos) {
+ case 0:
+ dev->rxfcs_rcvd = c << 8;
+ dev->rxpos++;
+ break;
+ case 1:
+ dev->rxfcs_rcvd |= c;
+ dev->rxpos++;
+ break;
+ case 2:
+ if (c != BYTE_FRAME) {
+ dev->rxstate = STATE_ERR;
+ } else {
+ mctp_serial_rx(dev);
+ dev->rxlen = 0;
+ dev->rxpos = 0;
+ dev->rxstate = STATE_IDLE;
+ }
+ break;
+ }
+}
+
+static void mctp_serial_push(struct mctp_serial *dev, unsigned char c)
+{
+ switch (dev->rxstate) {
+ case STATE_IDLE:
+ dev->rxstate = STATE_HEADER;
+ fallthrough;
+ case STATE_HEADER:
+ mctp_serial_push_header(dev, c);
+ break;
+
+ case STATE_ESCAPE:
+ c |= 0x20;
+ fallthrough;
+ case STATE_DATA:
+ if (dev->rxstate != STATE_ESCAPE && c == BYTE_ESC) {
+ dev->rxstate = STATE_ESCAPE;
+ } else {
+ dev->rxfcs = crc_ccitt_byte(dev->rxfcs, c);
+ dev->rxbuf[dev->rxpos] = c;
+ dev->rxpos++;
+ dev->rxstate = STATE_DATA;
+ if (dev->rxpos == dev->rxlen) {
+ dev->rxpos = 0;
+ dev->rxstate = STATE_TRAILER;
+ }
+ }
+ break;
+
+ case STATE_TRAILER:
+ mctp_serial_push_trailer(dev, c);
+ break;
+
+ case STATE_ERR:
+ if (c == BYTE_FRAME)
+ dev->rxstate = STATE_IDLE;
+ break;
+
+ default:
+ netdev_err_once(dev->netdev, "invalid rx state %d\n",
+ dev->rxstate);
+ }
+}
+
+static void mctp_serial_tty_receive_buf(struct tty_struct *tty,
+ const unsigned char *c,
+ const char *f, int len)
+{
+ struct mctp_serial *dev = tty->disc_data;
+ int i;
+
+ if (!netif_running(dev->netdev))
+ return;
+
+ /* we don't (currently) use the flag bytes, just data. */
+ for (i = 0; i < len; i++)
+ mctp_serial_push(dev, c[i]);
+}
+
+static const struct net_device_ops mctp_serial_netdev_ops = {
+ .ndo_start_xmit = mctp_serial_tx,
+};
+
+static void mctp_serial_setup(struct net_device *ndev)
+{
+ ndev->type = ARPHRD_MCTP;
+ ndev->mtu = MCTP_SERIAL_MTU;
+ ndev->hard_header_len = 0;
+ ndev->addr_len = 0;
+ ndev->tx_queue_len = DEFAULT_TX_QUEUE_LEN;
+ ndev->flags = IFF_NOARP;
+ ndev->netdev_ops = &mctp_serial_netdev_ops;
+ ndev->needs_free_netdev = true;
+}
+
+static int mctp_serial_open(struct tty_struct *tty)
+{
+ struct mctp_serial *dev;
+ struct net_device *ndev;
+ char name[32];
+ int idx, rc;
+
+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
+
+ if (!tty->ops->write)
+ return -EOPNOTSUPP;
+
+ if (tty->disc_data)
+ return -EEXIST;
+
+ idx = ida_alloc(&mctp_serial_ida, GFP_KERNEL);
+ if (idx < 0)
+ return idx;
+
+ snprintf(name, sizeof(name), "mctpserial%d", idx);
+ ndev = alloc_netdev(sizeof(*dev), name, NET_NAME_ENUM,
+ mctp_serial_setup);
+ if (!ndev) {
+ rc = -ENOMEM;
+ goto free_ida;
+ }
+
+ dev = netdev_priv(ndev);
+ dev->idx = idx;
+ dev->tty = tty;
+ dev->netdev = ndev;
+ dev->txstate = STATE_IDLE;
+ dev->rxstate = STATE_IDLE;
+ spin_lock_init(&dev->lock);
+ INIT_WORK(&dev->tx_work, mctp_serial_tx_work);
+
+ rc = register_netdev(ndev);
+ if (rc)
+ goto free_netdev;
+
+ tty->receive_room = 64 * 1024;
+ tty->disc_data = dev;
+
+ return 0;
+
+free_netdev:
+ free_netdev(ndev);
+
+free_ida:
+ ida_free(&mctp_serial_ida, idx);
+ return rc;
+}
+
+static void mctp_serial_close(struct tty_struct *tty)
+{
+ struct mctp_serial *dev = tty->disc_data;
+ int idx = dev->idx;
+
+ unregister_netdev(dev->netdev);
+ ida_free(&mctp_serial_ida, idx);
+}
+
+static struct tty_ldisc_ops mctp_ldisc = {
+ .owner = THIS_MODULE,
+ .num = N_MCTP,
+ .name = "mctp",
+ .open = mctp_serial_open,
+ .close = mctp_serial_close,
+ .receive_buf = mctp_serial_tty_receive_buf,
+ .write_wakeup = mctp_serial_tty_write_wakeup,
+};
+
+static int __init mctp_serial_init(void)
+{
+ return tty_register_ldisc(&mctp_ldisc);
+}
+
+static void __exit mctp_serial_exit(void)
+{
+ tty_unregister_ldisc(&mctp_ldisc);
+}
+
+module_init(mctp_serial_init);
+module_exit(mctp_serial_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Jeremy Kerr <jk@codeconstruct.com.au>");
+MODULE_DESCRIPTION("MCTP Serial transport");
projects / platform / kernel / linux-rpi.git / commitdiff