2 files changed, 112 insertions, 52 deletions

diff --git a/drivers/staging/comedi/drivers/ni_mio_common.c b/drivers/staging/comedi/drivers/ni_mio_common.c
index 0f97d7b611d7..9812508fe8d3 100644
--- a/drivers/staging/comedi/drivers/ni_mio_common.c
+++ b/drivers/staging/comedi/drivers/ni_mio_common.c
@@ -2729,66 +2729,36 @@ static int ni_ao_insn_write(struct comedi_device *dev,
 	return insn->n;
 }
 
-static int ni_ao_insn_config(struct comedi_device *dev,
-			     struct comedi_subdevice *s,
-			     struct comedi_insn *insn, unsigned int *data)
-{
-	const struct ni_board_struct *board = dev->board_ptr;
-	struct ni_private *devpriv = dev->private;
-	unsigned int nbytes;
-
-	switch (data[0]) {
-	case INSN_CONFIG_GET_HARDWARE_BUFFER_SIZE:
-		switch (data[1]) {
-		case COMEDI_OUTPUT:
-			nbytes = comedi_samples_to_bytes(s,
-							 board->ao_fifo_depth);
-			data[2] = 1 + nbytes;
-			if (devpriv->mite)
-				data[2] += devpriv->mite->fifo_size;
-			break;
-		case COMEDI_INPUT:
-			data[2] = 0;
-			break;
-		default:
-			return -EINVAL;
-		}
-		return 0;
-	default:
-		break;
-	}
-
-	return -EINVAL;
-}
-
-static int ni_ao_inttrig(struct comedi_device *dev,
-			 struct comedi_subdevice *s,
-			 unsigned int trig_num)
+/*
+ * Arms the AO device in preparation for a trigger event.
+ * This function also allocates and prepares a DMA channel (or FIFO if DMA is
+ * not used).  As a part of this preparation, this function preloads the DAC
+ * registers with the first values of the output stream.  This ensures that the
+ * first clock cycle after the trigger can be used for output.
+ *
+ * Note that this function _must_ happen after a user has written data to the
+ * output buffers via either mmap or write(fileno,...).
+ */
+static int ni_ao_arm(struct comedi_device *dev,
+		     struct comedi_subdevice *s)
 {
 	struct ni_private *devpriv = dev->private;
-	struct comedi_cmd *cmd = &s->async->cmd;
 	int ret;
 	int interrupt_b_bits;
 	int i;
 	static const int timeout = 1000;
 
 	/*
-	 * Require trig_num == cmd->start_arg when cmd->start_src == TRIG_INT.
-	 * For backwards compatibility, also allow trig_num == 0 when
-	 * cmd->start_src != TRIG_INT (i.e. when cmd->start_src == TRIG_EXT);
-	 * in that case, the internal trigger is being used as a pre-trigger
-	 * before the external trigger.
+	 * Prevent ao from doing things like trying to allocate the ao dma
+	 * channel multiple times.
 	 */
-	if (!(trig_num == cmd->start_arg ||
-	      (trig_num == 0 && cmd->start_src != TRIG_INT)))
+	if (!devpriv->ao_needs_arming) {
+		dev_dbg(dev->class_dev, "%s: device does not need arming!\n",
+			__func__);
 		return -EINVAL;
+	}
 
-	/*
-	 * Null trig at beginning prevent ao start trigger from executing more
-	 * than once per command (and doing things like trying to allocate the
-	 * ao dma channel multiple times).
-	 */
-	s->async->inttrig = NULL;
+	devpriv->ao_needs_arming = 0;
 
 	ni_set_bits(dev, NISTC_INTB_ENA_REG,
 		    NISTC_INTB_ENA_AO_FIFO | NISTC_INTB_ENA_AO_ERR, 0);
@@ -2840,6 +2810,75 @@ static int ni_ao_inttrig(struct comedi_device *dev,
 			   devpriv->ao_cmd1,
 		      NISTC_AO_CMD1_REG);
 
+	return 0;
+}
+
+static int ni_ao_insn_config(struct comedi_device *dev,
+			     struct comedi_subdevice *s,
+			     struct comedi_insn *insn, unsigned int *data)
+{
+	const struct ni_board_struct *board = dev->board_ptr;
+	struct ni_private *devpriv = dev->private;
+	unsigned int nbytes;
+
+	switch (data[0]) {
+	case INSN_CONFIG_GET_HARDWARE_BUFFER_SIZE:
+		switch (data[1]) {
+		case COMEDI_OUTPUT:
+			nbytes = comedi_samples_to_bytes(s,
+							 board->ao_fifo_depth);
+			data[2] = 1 + nbytes;
+			if (devpriv->mite)
+				data[2] += devpriv->mite->fifo_size;
+			break;
+		case COMEDI_INPUT:
+			data[2] = 0;
+			break;
+		default:
+			return -EINVAL;
+		}
+		return 0;
+	case INSN_CONFIG_ARM:
+		return ni_ao_arm(dev, s);
+	default:
+		break;
+	}
+
+	return -EINVAL;
+}
+
+static int ni_ao_inttrig(struct comedi_device *dev,
+			 struct comedi_subdevice *s,
+			 unsigned int trig_num)
+{
+	struct ni_private *devpriv = dev->private;
+	struct comedi_cmd *cmd = &s->async->cmd;
+	int ret;
+
+	/*
+	 * Require trig_num == cmd->start_arg when cmd->start_src == TRIG_INT.
+	 * For backwards compatibility, also allow trig_num == 0 when
+	 * cmd->start_src != TRIG_INT (i.e. when cmd->start_src == TRIG_EXT);
+	 * in that case, the internal trigger is being used as a pre-trigger
+	 * before the external trigger.
+	 */
+	if (!(trig_num == cmd->start_arg ||
+	      (trig_num == 0 && cmd->start_src != TRIG_INT)))
+		return -EINVAL;
+
+	/*
+	 * Null trig at beginning prevent ao start trigger from executing more
+	 * than once per command.
+	 */
+	s->async->inttrig = NULL;
+
+	if (devpriv->ao_needs_arming) {
+		/* only arm this device if it still needs arming */
+		ret = ni_ao_arm(dev, s);
+		if (ret)
+			return ret;
+	}
+
 	ni_stc_writew(dev, NISTC_AO_CMD2_START1_PULSE | devpriv->ao_cmd2,
 		      NISTC_AO_CMD2_REG);
 
@@ -3227,10 +3266,17 @@ static int ni_ao_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 	ni_ao_cmd_set_interrupts(dev, s);
 
 	/*
-	 * arm(ing) and star(ting) happen in ni_ao_inttrig, which _must_ be
-	 * called for ao commands since 1) TRIG_NOW is not supported and 2) DMA
-	 * must be setup and initially written to before arm/start happen.
+	 * arm(ing) must happen later so that DMA can be setup and DACs
+	 * preloaded with the actual output buffer before starting.
+	 *
+	 * start(ing) must happen _after_ arming is completed.  Starting can be
+	 * done either via ni_ao_inttrig, or via an external trigger.
+	 *
+	 * **Currently, ni_ao_inttrig will automatically attempt a call to
+	 * ni_ao_arm if the device still needs arming at that point.  This
+	 * allows backwards compatibility.
 	 */
+	devpriv->ao_needs_arming = 1;
 	return 0;
 }
 
diff --git a/drivers/staging/comedi/drivers/ni_stc.h b/drivers/staging/comedi/drivers/ni_stc.h
index 1966519cb6e5..f27b545f83eb 100644
--- a/drivers/staging/comedi/drivers/ni_stc.h
+++ b/drivers/staging/comedi/drivers/ni_stc.h
@@ -1053,6 +1053,20 @@ struct ni_private {
 	unsigned int is_67xx:1;
 	unsigned int is_6711:1;
 	unsigned int is_6713:1;
+
+	/*
+	 * Boolean value of whether device needs to be armed.
+	 *
+	 * Currently, only NI AO devices are known to be needing arming, since
+	 * the DAC registers must be preloaded before triggering.
+	 * This variable should only be set true during a command operation
+	 * (e.g ni_ao_cmd) and should then be set false by the arming
+	 * function (e.g. ni_ao_arm).
+	 *
+	 * This variable helps to ensure that multiple DMA allocations are not
+	 * possible.
+	 */
+	unsigned int ao_needs_arming:1;
 };
 
 static const struct comedi_lrange range_ni_E_ao_ext;