Shorten the derivation comment at the start

[elmcan.git] / module / elmcan.c

diff --git a/module/elmcan.c b/module/elmcan.c
index 94d031a70ef10ca564433eae3530c27b9eec3a97..4409642df1cbc1edcae56b3f92182ad1a93c56f4 100644 (file)
--- a/module/elmcan.c
+++ b/module/elmcan.c
@@ -2,8 +2,7 @@
 /* ELM327 based CAN interface driver (tty line discipline)
  *
  * This driver started as a derivative of linux/drivers/net/can/slcan.c
- * and my thanks go to the original authors for their inspiration, even
- * after almost none of their code is left.
+ * and my thanks go to the original authors for their inspiration.
  *
  * elmcan.c Author : Max Staudt <max-linux@enpas.org>
  * slcan.c Author  : Oliver Hartkopp <socketcan@hartkopp.net>
@@ -44,8 +43,8 @@
 #include <linux/can/rx-offload.h>
 
 /* Line discipline ID number.
- * N_DEVELOPMENT will likely be defined from Linux 5.18 onwards:
- * https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git/commit/?h=tty-next&id=c2faf737abfb10f88f2d2612d573e9edc3c42c37
+ * Starting with Linux v5.18-rc1, N_DEVELOPMENT is defined as 29:
+ * https://github.com/torvalds/linux/commit/c2faf737abfb10f88f2d2612d573e9edc3c42c37
  */
 #ifndef N_DEVELOPMENT
 #define N_DEVELOPMENT 29
@@ -58,7 +57,7 @@
 
 #define ELM327_NAPI_WEIGHT 4
 
-#define ELM327_SIZE_RXBUF 256
+#define ELM327_SIZE_RXBUF 224
 #define ELM327_SIZE_TXBUF 32
 
 #define ELM327_CAN_CONFIG_SEND_SFF           0x8000
@@ -89,6 +88,16 @@ struct elmcan {
 
        struct can_rx_offload offload;
 
+       /* TTY buffers */
+       u8 rxbuf[ELM327_SIZE_RXBUF];
+       u8 txbuf[ELM327_SIZE_TXBUF] ____cacheline_aligned;
+
+       /* TTY buffer accounting */
+       struct work_struct tx_work;     /* Flushes TTY TX buffer */
+       u8 *txhead;                     /* Next TX byte */
+       unsigned txleft;                /* Bytes left to TX */
+       int rxfill;                     /* Bytes already RX'd in buffer */
+
        /* TTY and netdev devices that we're bridging */
        struct tty_struct *tty;
        struct net_device *dev;
@@ -96,23 +105,6 @@ struct elmcan {
        /* Per-channel lock */
        spinlock_t lock;
 
-       /* Stop the channel on UART side hardware failure, e.g. stray
-        * characters or neverending lines. This may be caused by bad
-        * UART wiring, a bad ELM327, a bad UART bridge...
-        * Once this is true, nothing will be sent to the TTY.
-        */
-       bool uart_side_failure;
-
-       /* TTY TX helpers */
-       struct work_struct tx_work;     /* Flushes TTY TX buffer   */
-       u8 *txbuf;                      /* Pointer to our TX buffer */
-       u8 *txhead;                     /* Pointer to next TX byte */
-       unsigned txleft;                /* Bytes left to TX */
-
-       /* TTY RX helpers */
-       u8 rxbuf[ELM327_SIZE_RXBUF];
-       int rxfill;
-
        /* State machine */
        enum {
                ELM327_STATE_NOTINIT = 0,
@@ -121,7 +113,9 @@ struct elmcan {
                ELM327_STATE_RECEIVING,
        } state;
 
-       bool drop_next_line;
+       /* Things we have yet to send */
+       char **next_init_cmd;
+       unsigned long cmds_todo;
 
        /* The CAN frame and config the ELM327 is sending/using,
         * or will send/use after finishing all cmds_todo
@@ -130,9 +124,15 @@ struct elmcan {
        u16 can_config;
        u8 can_bitrate_divisor;
 
-       /* Things we have yet to send */
-       char **next_init_cmd;
-       unsigned long cmds_todo;
+       /* Parser state */
+       bool drop_next_line;
+
+       /* Stop the channel on UART side hardware failure, e.g. stray
+        * characters or neverending lines. This may be caused by bad
+        * UART wiring, a bad ELM327, a bad UART bridge...
+        * Once this is true, nothing will be sent to the TTY.
+        */
+       bool uart_side_failure;
 };
 
 static inline void elm327_uart_side_failure(struct elmcan *elm);
@@ -160,9 +160,7 @@ static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
        elm->txleft = len - written;
        elm->txhead = elm->txbuf + written;
 
-       if (!elm->txleft)
-               netif_wake_queue(elm->dev);
-       else
+       if (elm->txleft)
                set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
 }
 
@@ -572,6 +570,11 @@ static void elm327_handle_prompt(struct elmcan *elm)
                elm327_send(elm, "ATMA\r", 5);
                elm->state = ELM327_STATE_RECEIVING;
 
+               /* We will be in the default state once this command is
+                * send, so enable the TX packet queue.
+                */
+               netif_wake_queue(elm->dev);
+
                return;
        }
 
@@ -645,6 +648,11 @@ static void elm327_handle_prompt(struct elmcan *elm)
 
                elm->drop_next_line = 1;
                elm->state = ELM327_STATE_RECEIVING;
+
+               /* We will be in the default state once this command is
+                * send, so enable the TX packet queue.
+                */
+               netif_wake_queue(elm->dev);
        }
 
        elm327_send(elm, local_txbuf, strlen(local_txbuf));
@@ -823,15 +831,12 @@ static int elmcan_netdev_close(struct net_device *dev)
        elm327_send(elm, ELM327_DUMMY_STRING, 1);
        spin_unlock_bh(&elm->lock);
 
-       /* Give UART one final chance to flush.
-        * This may netif_wake_queue(), so don't netif_stop_queue()
-        * before flushing the worker.
-        */
+       netif_stop_queue(dev);
+
+       /* Give UART one final chance to flush. */
        clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
        flush_work(&elm->tx_work);
 
-       netif_stop_queue(dev);
-
        can_rx_offload_disable(&elm->offload);
        elm->can.state = CAN_STATE_STOPPED;
        can_rx_offload_del(&elm->offload);
@@ -1003,7 +1008,6 @@ static void elmcan_ldisc_tx_worker(struct work_struct *work)
        if (!elm->txleft)  {
                clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
                spin_unlock_bh(&elm->lock);
-               netif_wake_queue(elm->dev);
        } else {
                spin_unlock_bh(&elm->lock);
        }
@@ -1055,12 +1059,6 @@ static int elmcan_ldisc_open(struct tty_struct *tty)
                return -ENFILE;
        elm = netdev_priv(dev);
 
-       elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
-       if (!elm->txbuf) {
-               err = -ENOMEM;
-               goto out_err;
-       }
-
        /* Configure TTY interface */
        tty->receive_room = 65536; /* We don't flow control */
        spin_lock_init(&elm->lock);
@@ -1092,7 +1090,6 @@ static int elmcan_ldisc_open(struct tty_struct *tty)
        return 0;
 
 out_err:
-       kfree(elm->txbuf);
        free_candev(elm->dev);
        return err;
 }
@@ -1122,7 +1119,6 @@ static void elmcan_ldisc_close(struct tty_struct *tty)
 
        netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
 
-       kfree(elm->txbuf);
        free_candev(elm->dev);
 }