It is also required to use semaphore release instead of flush when stopping
or on BUSOFF/AHBERR condition. Otherwise a task just about to wait
(taking the semaphore) could end up locked because the semaphore count is
still the same.
There was previously a scenario where the semaphore flush would not always make
semaphore obtain to return in case of BUSOFF, AHBERROR or grcan_stop. It has to
do with the rtems_semaphore_flush() not releasing the semaphore but just aborts
any _current_ waiter.
---
c/src/lib/libbsp/sparc/shared/can/grcan.c | 62 ++++++++++++++++---------------
1 file changed, 32 insertions(+), 30 deletions(-)
diff --git a/c/src/lib/libbsp/sparc/shared/can/grcan.c
b/c/src/lib/libbsp/sparc/shared/can/grcan.c
index 1050934..ac1c718 100644
--- a/c/src/lib/libbsp/sparc/shared/can/grcan.c
+++ b/c/src/lib/libbsp/sparc/shared/can/grcan.c
@@ -492,15 +492,19 @@ static void grcan_hw_stop(struct grcan_priv *pDev)
static void grcan_sw_stop(struct grcan_priv *pDev)
{
- /* Reset semaphores to the initial state and wakeing
- * all threads waiting for an IRQ. The threads that
- * get woken up must check for RTEMS_UNSATISFIED in
+ /*
+ * Release semaphores to wake all threads waiting for an IRQ.
+ * The threads that
+ * get woken up must check started state in
* order to determine that they should return to
* user space with error status.
+ *
+ * Entering into started mode again will reset the
+ * semaphore count.
*/
- rtems_semaphore_flush(pDev->rx_sem);
- rtems_semaphore_flush(pDev->tx_sem);
- rtems_semaphore_flush(pDev->txempty_sem);
+ rtems_semaphore_release(pDev->rx_sem);
+ rtems_semaphore_release(pDev->tx_sem);
+ rtems_semaphore_release(pDev->txempty_sem);
}
static void grcan_hw_config(struct grcan_regs *regs, struct grcan_config *conf)
@@ -962,17 +966,14 @@ static int grcan_wait_rxdata(struct grcan_priv *pDev, int
min)
/* Wait for IRQ to fire only if has been triggered */
if (wait) {
- if (
- rtems_semaphore_obtain(
- pDev->rx_sem,
- RTEMS_WAIT,
- RTEMS_NO_TIMEOUT
- ) == RTEMS_UNSATISFIED
- ) {
- DBGC(DBG_STATE, "UNSATISFIED\n");
- /* Device driver has been closed or stopped, return
with error status */
- return state2err[pDev->started];
- }
+ rtems_semaphore_obtain(pDev->rx_sem, RTEMS_WAIT,
RTEMS_NO_TIMEOUT);
+ /*
+ * The semaphore is released either due to the expected IRQ
+ * condition or by BUSOFF, AHBERROR or another thread calling
+ * grcan_stop(). In either case, state2err[] has the correnct
+ * return value.
+ */
+ return state2err[pDev->started];
}
return 0;
@@ -1054,13 +1055,8 @@ static int grcan_wait_txspace(struct grcan_priv *pDev,
int min)
/* Wait for IRQ to fire only if it has been triggered */
if (wait) {
- if (rtems_semaphore_obtain(pDev->tx_sem, RTEMS_WAIT,
RTEMS_NO_TIMEOUT) ==
- RTEMS_UNSATISFIED) {
- /* Device driver has flushed us, this may be due to
another thread has
- * closed the device, this is to avoid deadlock */
- DBGC(DBG_STATE, "UNSATISFIED\n");
- return state2err[pDev->started];
- }
+ rtems_semaphore_obtain(pDev->tx_sem, RTEMS_WAIT,
RTEMS_NO_TIMEOUT);
+ return state2err[pDev->started];
}
/* At this point the TxIRQ has been masked, we ned not to mask it */
@@ -1117,11 +1113,10 @@ static int grcan_tx_flush(struct grcan_priv *pDev)
break;
/* Wait for IRQ to wake us */
- if (rtems_semaphore_obtain
- (pDev->txempty_sem, RTEMS_WAIT,
- RTEMS_NO_TIMEOUT) == RTEMS_UNSATISFIED) {
- DBGC(DBG_STATE, "UNSATISFIED\n");
- return state2err[pDev->started];
+ rtems_semaphore_obtain(pDev->txempty_sem, RTEMS_WAIT,
RTEMS_NO_TIMEOUT);
+ state = pDev->started;
+ if (state != STATE_STARTED) {
+ return state2err[state];
}
}
return 0;
@@ -1565,6 +1560,13 @@ int grcan_start(void *d)
return -2;
}
+ /* Clear semaphore state. This is to avoid effects from previous
+ * bus-off/stop where semahpores where flushed() but the count remained.
+ */
+ rtems_semaphore_obtain(pDev->rx_sem, RTEMS_NO_WAIT, 0);
+ rtems_semaphore_obtain(pDev->tx_sem, RTEMS_NO_WAIT, 0);
+ rtems_semaphore_obtain(pDev->txempty_sem, RTEMS_NO_WAIT, 0);
+
/* Read and write are now open... */
pDev->started = STATE_STARTED;
DBGC(DBG_STATE, "STOPPED|BUSOFF|AHBERR->STARTED\n");
@@ -1942,7 +1944,7 @@ static void grcan_interrupt(void *arg)
*/
SPIN_UNLOCK(&pDev->devlock, irqflags);
- /* flush semaphores to wake blocked threads */
+ /* Release semaphores to wake blocked threads. */
grcan_sw_stop(pDev);
/*
--
2.7.4
_______________________________________________
devel mailing list
devel@rtems.org
http://lists.rtems.org/mailman/listinfo/devel
