From 7cb931ffb44a39c9b6b8c16e3aba7a61d808ddb3 Mon Sep 17 00:00:00 2001 From: norly Date: Tue, 19 Feb 2019 23:47:35 +0100 Subject: [PATCH] Comments and minor style --- module/elmcan.c | 121 ++++++++++++++++-------------------------------- 1 file changed, 40 insertions(+), 81 deletions(-) diff --git a/module/elmcan.c b/module/elmcan.c index f9f6c72..b85c1c2 100644 --- a/module/elmcan.c +++ b/module/elmcan.c @@ -194,11 +194,7 @@ static void elm327_send(struct elmcan *elm, const void *buf, size_t len) } -/* - * Take the ELM327 out of almost any state and back into command mode - * - * Assumes elm->lock taken. - */ +/* Take the ELM327 out of almost any state and back into command mode. */ static void elm327_kick_into_cmd_mode(struct elmcan *elm) { if (elm->state != ELM_GETMAGICCHAR && elm->state != ELM_GETPROMPT) { @@ -209,12 +205,7 @@ static void elm327_kick_into_cmd_mode(struct elmcan *elm) } -/* - * Schedule a CAN frame, and any necessary config changes, - * to be sent down the TTY. - * - * Assumes elm->lock taken. - */ +/* Schedule a CAN frame and necessary config changes to be sent to the TTY. */ static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame) { /* Schedule any necessary changes in ELM327's CAN configuration */ @@ -393,8 +384,8 @@ static void elm327_parse_error(struct elmcan *elm, int len) if (!memcmp(elm->rxbuf, "BUFFER FULL", 11)) { /* This case will only happen if the last data * line was complete. - * Otherwise, elm327_parse_frame() will emit the - * error frame instead. + * Otherwise, elm327_parse_frame() will heuristically + * emit this error frame instead. */ frame.can_id |= CAN_ERR_CRTL; frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW; @@ -434,6 +425,18 @@ static void elm327_parse_error(struct elmcan *elm, int len) } +/* Parse CAN frames coming as ASCII from ELM327. + * They can be of various formats: + * + * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL + * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL + * + * where D = DLC, PL = payload byte + * + * Instead of a payload, RTR indicates a remote request. + * + * We will use the spaces and line length to guess the format. + */ static int elm327_parse_frame(struct elmcan *elm, int len) { struct can_frame frame; @@ -523,13 +526,13 @@ static int elm327_parse_frame(struct elmcan *elm, int len) /* Check for RTR frame */ if (elm->rxfill >= hexlen + 3 - && elm->rxbuf[hexlen + 0] == 'R' - && elm->rxbuf[hexlen + 1] == 'T' - && elm->rxbuf[hexlen + 2] == 'R') { + && !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) { frame.can_id |= CAN_RTR_FLAG; } - /* Is the line long enough to hold the advertised payload? */ + /* Is the line long enough to hold the advertised payload? + * Note: RTR frames have a DLC, but no actual payload. + */ if (!(frame.can_id & CAN_RTR_FLAG) && (hexlen < frame.can_dlc * 3 + datastart)) { /* Incomplete frame. */ @@ -593,7 +596,6 @@ static void elm327_parse_line(struct elmcan *elm, int len) } } - static void elm327_handle_prompt(struct elmcan *elm) { struct can_frame *frame = &elm->can_frame; @@ -679,14 +681,12 @@ static bool elm327_is_ready_char(char c) return (c & 0x3f) == ELM327_READY_CHAR; } - static void elm327_drop_bytes(struct elmcan *elm, int i) { memmove(&elm->rxbuf[0], &elm->rxbuf[i], sizeof(elm->rxbuf) - i); elm->rxfill -= i; } - static void elm327_parse_rxbuf(struct elmcan *elm) { int len; @@ -783,7 +783,6 @@ static void elm327_parse_rxbuf(struct elmcan *elm) * (takes elm->lock) * ************************************************************************/ -/* Netdevice DOWN -> UP routine */ static int elmcan_netdev_open(struct net_device *dev) { struct elmcan *elm = netdev_priv(dev); @@ -808,7 +807,6 @@ static int elmcan_netdev_open(struct net_device *dev) return err; } - /* Initialize the ELM327 */ elm327_init(elm); spin_unlock_bh(&elm->lock); @@ -819,15 +817,12 @@ static int elmcan_netdev_open(struct net_device *dev) return 0; } -/* Netdevice UP -> DOWN routine */ static int elmcan_netdev_close(struct net_device *dev) { struct elmcan *elm = netdev_priv(dev); spin_lock_bh(&elm->lock); if (elm->tty) { - /* TTY discipline is running. */ - /* Interrupt whatever we're doing right now */ elm327_send(elm, ELM327_MAGIC_STRING, 1); @@ -851,7 +846,7 @@ static int elmcan_netdev_close(struct net_device *dev) return 0; } -/* Send a can_frame to a TTY queue. */ +/* Send a can_frame to a TTY. */ static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb, struct net_device *dev) { @@ -877,6 +872,7 @@ static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb, WARN_ON(elm->hw_failure); if (elm->tty == NULL + || elm->hw_failure || elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) { spin_unlock(&elm->lock); goto out; @@ -919,19 +915,17 @@ static const struct net_device_ops elmcan_netdev_ops = { * (takes elm->lock) * ************************************************************************/ -/* - * Get a reference to our struct, taking into account locks/refcounts. +/* Get a reference to our struct, taking into account locks/refcounts. * This is to ensure ordering in case we are shutting down, and to ensure - * there is a refcount at all (because tty->disc_data may be NULL). + * there is a refcount at all (otherwise tty->disc_data may be freed and + * before we increment the refcount). + * Use this for anything that can race against elmcan_ldisc_close(). */ static struct elmcan *get_elm(struct tty_struct *tty) { struct elmcan *elm; bool got_ref; - /* Lock all elmcan TTYs, so tty->disc_data can't become NULL - * the moment before we increase the reference counter. - */ spin_lock_bh(&elmcan_discdata_lock); elm = (struct elmcan *) tty->disc_data; @@ -955,14 +949,9 @@ static void put_elm(struct elmcan *elm) } - -/* - * Handle the 'receiver data ready' interrupt. - * This function is called by the 'tty_io' module in the kernel when - * a block of ELM327 CAN data has been received, which can now be parsed - * and sent on to some IP layer for further processing. This will not - * be re-entered while running but other ldisc functions may be called - * in parallel +/* Handle incoming ELM327 ASCII data. + * This will not be re-entered while running, but other ldisc + * functions may be called in parallel. */ static void elmcan_ldisc_rx(struct tty_struct *tty, const unsigned char *cp, char *fp, int count) @@ -980,7 +969,6 @@ static void elmcan_ldisc_rx(struct tty_struct *tty, return; } - /* Read the characters out of the buffer */ while (count-- && elm->rxfill < sizeof(elm->rxbuf)) { if (fp && *fp++) { netdev_err(elm->dev, "Error in received character stream. Check your wiring."); @@ -999,7 +987,7 @@ static void elmcan_ldisc_rx(struct tty_struct *tty, */ if (*cp != 0) { /* Check for stray characters on the UART line. - * No idea what causes this. + * Likely caused by bad hardware. */ if (!accept_flaky_uart && !isdigit(*cp) @@ -1014,10 +1002,6 @@ static void elmcan_ldisc_rx(struct tty_struct *tty, && '?' != *cp && '\r' != *cp && ' ' != *cp) { - /* We've received an invalid character, so bail. - * There's something wrong with the ELM327, or - * with the UART line. - */ netdev_err(elm->dev, "Received illegal character %02x.\n", *cp); @@ -1050,14 +1034,14 @@ static void elmcan_ldisc_rx(struct tty_struct *tty, put_elm(elm); } -/* - * Write out remaining transmit buffer. + +/* Write out remaining transmit buffer. * Scheduled when TTY is writable. */ static void elmcan_ldisc_tx_worker(struct work_struct *work) { /* No need to use get_elm() here, as we'll always flush workers - * befory destroying the elmcan object. + * before destroying the elmcan object. */ struct elmcan *elm = container_of(work, struct elmcan, tx_work); ssize_t actual; @@ -1075,7 +1059,7 @@ static void elmcan_ldisc_tx_worker(struct work_struct *work) if (elm->txleft <= 0) { /* Our TTY write buffer is empty: - * We can start transmission of another packet + * Allow netdev to hand us another packet */ clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags); spin_unlock_bh(&elm->lock); @@ -1098,11 +1082,7 @@ static void elmcan_ldisc_tx_worker(struct work_struct *work) spin_unlock_bh(&elm->lock); } - -/* - * Called by the driver when there's room for more data. - * Schedule the transmit. - */ +/* Called by the driver when there's room for more data. */ static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty) { struct elmcan *elm = get_elm(tty); @@ -1116,7 +1096,6 @@ static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty) } - /* ELM327 can only handle bitrates that are integer divisors of 500 kHz, * or 7/8 of that. Divisors are 1 to 64. * Currently we don't implement support for 7/8 rates. @@ -1132,22 +1111,14 @@ static const u32 elmcan_bitrate_const[64] = { 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000 }; -/* Dummy function to claim we're changing the bitrate. - * We actually do this when opening the net device. - */ + +/* Dummy needed to use bitrate_const */ static int elmcan_do_set_bittiming(struct net_device *netdev) { return 0; } -/* - * Open the high-level part of the elmcan channel. - * This function is called by the TTY module when the - * elmcan line discipline is called for. - * - * Called in process context serialized from other ldisc calls. - */ static int elmcan_ldisc_open(struct tty_struct *tty) { struct net_device *dev; @@ -1161,7 +1132,6 @@ static int elmcan_ldisc_open(struct tty_struct *tty) return -EOPNOTSUPP; - /* OK. Find a free elmcan channel to use. */ dev = alloc_candev(sizeof(struct elmcan), 0); if (!dev) return -ENFILE; @@ -1203,8 +1173,7 @@ static int elmcan_ldisc_open(struct tty_struct *tty) return 0; } -/* - * Close down an elmcan channel. +/* Close down an elmcan channel. * This means flushing out any pending queues, and then returning. * This call is serialized against other ldisc functions: * Once this is called, no other ldisc function of ours is entered. @@ -1213,15 +1182,12 @@ static int elmcan_ldisc_open(struct tty_struct *tty) */ static void elmcan_ldisc_close(struct tty_struct *tty) { - /* Use get_elm() to synchronize against other users */ struct elmcan *elm = get_elm(tty); if (!elm) return; - /* Tear down network side. - * unregister_netdev() calls .ndo_stop() so we don't have to. - */ + /* unregister_netdev() calls .ndo_stop() so we don't have to. */ unregister_candev(elm->dev); /* Decrease the refcount twice, once for our own get_elm(), @@ -1231,13 +1197,10 @@ static void elmcan_ldisc_close(struct tty_struct *tty) put_elm(elm); put_elm(elm); - /* Spin until refcount reaches 0 */ while (atomic_read(&elm->refcount) > 0) msleep_interruptible(10); - /* At this point, all ldisc calls to us will be no-ops. - * Since the refcount is 0, they are bailing immediately. - */ + /* At this point, all ldisc calls to us have become no-ops. */ /* Mark channel as dead */ spin_lock_bh(&elm->lock); @@ -1245,12 +1208,10 @@ static void elmcan_ldisc_close(struct tty_struct *tty) elm->tty = NULL; spin_unlock_bh(&elm->lock); - /* Flush TTY side */ flush_work(&elm->tx_work); netdev_info(elm->dev, "elmcan off %s.\n", tty->name); - /* Free our memory */ free_candev(elm->dev); } @@ -1260,7 +1221,6 @@ static int elmcan_ldisc_hangup(struct tty_struct *tty) return 0; } -/* Perform I/O control on an active elmcan channel. */ static int elmcan_ldisc_ioctl(struct tty_struct *tty, struct file *file, unsigned int cmd, unsigned long arg) { @@ -1318,7 +1278,6 @@ static int __init elmcan_init(void) pr_info("ELM327 based best-effort CAN interface driver\n"); pr_info("This device is severely limited as a CAN interface, see documentation.\n"); - /* Fill in our line protocol discipline, and register it */ status = tty_register_ldisc(N_ELMCAN, &elmcan_ldisc); if (status) pr_err("can't register line discipline\n"); -- 2.30.2