sched/semaphore: Add an internal interface to reset a semaphore count.

ChangeLog

@@ -11536,4 +11536,7 @@
 	* configs/sabre-6quad:  Placeholder that will eventually become board support
 	  for the NXP/Freescale Sabre 6Quad board (2016-02-28).
 	* arch/arm/src/stm32:  Support for STM32F46xx from Paul Alexander Patience
-	  (2016-03-01).
+	* sched/semaphore/sem_reset.c and include/nuttx/semaphore.h: Add an internal,
+	  non-standard interface to reset a semaphore count.  This is sometimes
+	  needed by drivers in order to recover from error conditions (2016-03-05)
+

arch

@@ -1 +1 @@
-Subproject commit 7fe684d488ea88c31b2a155690de8beb7345f913
+Subproject commit 0b8fe68bf5c15b49d7877c97516fdda542b2149b

configs

@@ -1 +1 @@
-Subproject commit bc95bb361c0963b69782cc77cec251d047eadb0d
+Subproject commit 0c764446fee7b6b4c6bb9c188042fb98b4d1e8eb

include/nuttx/semaphore.h

@@ -113,6 +113,24 @@ extern "C"
 
 int sem_tickwait(FAR sem_t *sem, systime_t start, uint32_t delay);
 
+/****************************************************************************
+ * Name: sem_reset
+ *
+ * Description:
+ *   Reset a semaphore to a specific value.  This kind of operation is
+ *   sometimes required for certain error handling conditions.
+ *
+ * Parameters:
+ *   sem   - Semaphore descriptor to be reset
+ *   count - The requested semaphore count
+ *
+ * Return Value:
+ *   0 (OK) or a negated errno value if unsuccessful
+ *
+ ****************************************************************************/
+
+int sem_reset(FAR sem_t *sem, int16_t count);
+
 #undef EXTERN
 #ifdef __cplusplus
 }

sched/semaphore/Make.defs

@@ -1,7 +1,7 @@
 ############################################################################
 # sched/semaphore/Make.defs
 #
-#   Copyright (C) 2014-2015 Gregory Nutt. All rights reserved.
+#   Copyright (C) 2014-2016 Gregory Nutt. All rights reserved.
 #   Author: Gregory Nutt <gnutt@nuttx.org>
 #
 # Redistribution and use in source and binary forms, with or without
@@ -35,7 +35,7 @@
 
 CSRCS += sem_destroy.c sem_wait.c sem_trywait.c sem_tickwait.c
 CSRCS += sem_timedwait.c sem_timeout.c sem_post.c sem_recover.c
-CSRCS += sem_waitirq.c
+CSRCS += sem_reset.c sem_waitirq.c
 
 ifeq ($(CONFIG_PRIORITY_INHERITANCE),y)
 CSRCS += sem_initialize.c sem_holder.c

sched/semaphore/sem_reset.c

@@ -0,0 +1,121 @@
+/****************************************************************************
+ * sched/semaphore/sem_reset.c
+ *
+ *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <semaphore.h>
+#include <sched.h>
+#include <assert.h>
+
+#include <nuttx/irq.h>
+
+#include "semaphore/semaphore.h"
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: sem_reset
+ *
+ * Description:
+ *   Reset a semaphore to a specific value.  This kind of operation is
+ *   sometimes required for certain error handling conditions.
+ *
+ * Parameters:
+ *   sem   - Semaphore descriptor to be reset
+ *   count - The requested semaphore count
+ *
+ * Return Value:
+ *   0 (OK) or a negated errno value if unsuccessful
+ *
+ ****************************************************************************/
+
+int sem_reset(FAR sem_t *sem, int16_t count)
+{
+  irqstate_t flags;
+
+  DEBUGASSERT(sem != NULL && count >= 0);
+
+  /* Don't allow any context switches that may result from the following
+   * sem_post operations.
+   */
+
+  sched_lock();
+
+  /* Prevent any access to the semaphore by interrupt handlers while we are
+   * performing this operation.
+   */
+
+  flags = enter_critical_section();
+
+  /* A negative count indicates the negated number of threads that are
+   * waiting to take a count from the semaphore.  Loop here, handing
+   * out counts to any waiting threads.
+   */
+
+  while (sem->semcount < 0 && count > 0)
+    {
+      /* Give out one counting, waking up one of the waiting threads
+       * and, perhaps, kicking off a lot of priority inheritance
+       * logic (REVISIT).
+       */
+
+      DEBUGVERIFY(sem_post(sem));
+      count--;
+    }
+
+  /* We exit the above loop with either (1) no threads waiting for the
+   * (i.e., with sem->semcount >= 0).  In this case, 'count' holds the
+   * the new value of the semaphore count.  OR (2) with threads still
+   * waiting but all of the semaphore counts exhausted:  The current
+   * value of sem->semcount is correct.
+   */
+
+  if (sem->semcount >= 0)
+    {
+      sem->semcount = count;
+    }
+
+  /* Allow any pending context switches to occur now */
+
+  leave_critical_section(flags);
+  sched_unlock();
+  return OK;
+}