Separate buffers from struct elm

This avoids trouble with CPU caches racing DMA accesses on ARM.

diff --git a/module/elmcan.c b/module/elmcan.c
index ba4ef0d710ca00bf2d59b0b666837b8d3446e69f..7ac1f5466a052a3c6e889e830fc6927313fc8b42 100644 (file)
--- a/module/elmcan.c
+++ b/module/elmcan.c
@@ -60,6 +60,9 @@ MODULE_PARM_DESC(accept_flaky_uart, "Don't bail at the first invalid character.
 #define N_ELMCAN 29
 #endif
 
+#define ELM327_SIZE_RXBUF 256
+#define ELM327_SIZE_TXBUF 32
+
 #define ELM327_CAN_CONFIG_SEND_SFF           0x8000
 #define ELM327_CAN_CONFIG_VARIABLE_DLC       0x4000
 #define ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF  0x2000
@@ -111,12 +114,12 @@ struct elmcan {
 
        /* TTY TX helpers */
        struct work_struct      tx_work;        /* Flushes TTY TX buffer   */
-       unsigned char           txbuf[32];
+       unsigned char           *txbuf;
        unsigned char           *txhead;        /* Pointer to next TX byte */
        int                     txleft;         /* Bytes left to TX */
 
        /* TTY RX helpers */
-       unsigned char rxbuf[256];
+       unsigned char *rxbuf;
        int rxfill;
 
        /* State machine */
@@ -687,7 +690,7 @@ static bool elm327_is_ready_char(char c)
 
 static void elm327_drop_bytes(struct elmcan *elm, int i)
 {
-       memmove(&elm->rxbuf[0], &elm->rxbuf[i], sizeof(elm->rxbuf) - i);
+       memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
        elm->rxfill -= i;
 }
 
@@ -739,7 +742,7 @@ static void elm327_parse_rxbuf(struct elmcan *elm)
                        /* empty loop */
                }
 
-               if (len == sizeof(elm->rxbuf)) {
+               if (len == ELM327_SIZE_RXBUF) {
                        /* Line exceeds buffer. It's probably all garbage.
                         * Did we even connect at the right baud rate?
                         */
@@ -984,7 +987,7 @@ static void elmcan_ldisc_rx(struct tty_struct *tty,
                goto out;
        }
 
-       while (count-- && elm->rxfill < sizeof(elm->rxbuf)) {
+       while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
                if (fp && *fp++) {
                        netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
 
@@ -1137,6 +1140,13 @@ static int elmcan_ldisc_open(struct tty_struct *tty)
                return -ENFILE;
        elm = netdev_priv(dev);
 
+       elm->rxbuf = kmalloc(ELM327_SIZE_RXBUF, GFP_KERNEL);
+       elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
+       if (!elm->rxbuf || !elm->txbuf) {
+               err = -ENOMEM;
+               goto out_err;
+       }
+
        /* Configure TTY interface */
        tty->receive_room = 65536; /* We don't flow control */
        elm->txleft = 0; /* Clear TTY TX buffer */
@@ -1163,14 +1173,20 @@ static int elmcan_ldisc_open(struct tty_struct *tty)
 
        /* Let 'er rip */
        err = register_candev(elm->dev);
-       if (err) {
-               free_candev(elm->dev);
-               return err;
-       }
+       if (err)
+               goto out_err;
 
        netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
 
        return 0;
+
+out_err:
+       if (elm->txbuf)
+               kfree(elm->txbuf);
+       if (elm->rxbuf)
+               kfree(elm->rxbuf);
+       free_candev(elm->dev);
+       return err;
 }
 
 /* Close down an elmcan channel.
@@ -1212,6 +1228,8 @@ static void elmcan_ldisc_close(struct tty_struct *tty)
 
        netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
 
+       kfree(elm->txbuf);
+       kfree(elm->rxbuf);
        free_candev(elm->dev);
 }
 

diff --git a/readme.rst b/readme.rst
index 9924167e59f7073867be5f9a031775ccc7a92eab..a283e0af7ee148b72a72dc58821ffb0796c3e1fd 100644 (file)
--- a/readme.rst
+++ b/readme.rst
@@ -341,8 +341,5 @@ termination resistors on its PCB and try removing them.
 To Do list for future development
 ----------------------------------
 
-- DMA capable rx/tx buffers
-  (is this relevant for this driver?)
-
 - flushing of ``tx_work`` is too late in ``ldisc_close()``
   (is this still the case?)