staging: comedi: comedi_test: implement commands on AO subdevice

Implement COMEDI asynchronous commands on the fake analog output
subdevice.  This is useful for testing asynchronous commands in the
"write" direction when no real hardware is available.

A normal kernel timer is used to drive the command.  The new timer
expiry function `waveform_ao_timer()` handles whole "scans" at a time
according to the number of scan period that have elapsed since the last
scan.  Data for each channel in the scan is written to the internal
loopback array `devpriv->ao_loopbacks[]` and can be read back on the
analog input channels.  However, if several scan periods are outstanding
in the timer expiry function, only the latest available scan data is
written to the loopback array in order to save processing time.  The
expiry function also checks for underrun conditions, and checks for
normal termination of the asynchronous command when a "stop" scan count
is reached.

After the command is tested by `waveform_ao_cmdtest()` and set up by
`waveform_ao_cmd()`, it is not started until an internal trigger
function `waveform_ao_inttrig_start()` is called as a result of the user
performing an `INSN_INTTRIG` instruction on the subdevice.  The command
is stopped when the "cancel" handler `waveform_ao_cancel()` is called.
This may be due to the command terminating due to completion or an
error, or as a result of the user cancelling the command.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/comedi_test.c

@@ -57,7 +57,8 @@
 #define N_CHANS 8
 
 enum waveform_state_bits {
-	WAVEFORM_AI_RUNNING = 0
+	WAVEFORM_AI_RUNNING,
+	WAVEFORM_AO_RUNNING
 };
 
 /* Data unique to this driver */
@@ -70,6 +71,9 @@ struct waveform_private {
 	unsigned long state_bits;
 	unsigned int ai_scan_period;	/* AI scan period in usec */
 	unsigned int ai_convert_period;	/* AI conversion period in usec */
+	struct timer_list ao_timer;	/* timer for AO commands */
+	u64 ao_last_scan_time;		/* time of previous AO scan in usec */
+	unsigned int ao_scan_period;	/* AO scan period in usec */
 	unsigned short ao_loopbacks[N_CHANS];
 };
 
@@ -417,6 +421,201 @@ static int waveform_ai_insn_read(struct comedi_device *dev,
 	return insn->n;
 }
 
+/*
+ * This is the background routine to handle AO commands, scheduled by
+ * a timer mechanism.
+ */
+static void waveform_ao_timer(unsigned long arg)
+{
+	struct comedi_device *dev = (struct comedi_device *)arg;
+	struct waveform_private *devpriv = dev->private;
+	struct comedi_subdevice *s = dev->write_subdev;
+	struct comedi_async *async = s->async;
+	struct comedi_cmd *cmd = &async->cmd;
+	u64 now;
+	u64 scans_since;
+	unsigned int scans_avail = 0;
+
+	/* check command is still active */
+	if (!test_bit(WAVEFORM_AO_RUNNING, &devpriv->state_bits))
+		return;
+
+	/* determine number of scan periods since last time */
+	now = ktime_to_us(ktime_get());
+	scans_since = now - devpriv->ao_last_scan_time;
+	do_div(scans_since, devpriv->ao_scan_period);
+	if (scans_since) {
+		unsigned int i;
+
+		/* determine scans in buffer, limit to scans to do this time */
+		scans_avail = comedi_nscans_left(s, 0);
+		if (scans_avail > scans_since)
+			scans_avail = scans_since;
+		if (scans_avail) {
+			/* skip all but the last scan to save processing time */
+			if (scans_avail > 1) {
+				unsigned int skip_bytes, nbytes;
+
+				skip_bytes =
+				comedi_samples_to_bytes(s, cmd->scan_end_arg *
+							   (scans_avail - 1));
+				nbytes = comedi_buf_read_alloc(s, skip_bytes);
+				comedi_buf_read_free(s, nbytes);
+				comedi_inc_scan_progress(s, nbytes);
+				if (nbytes < skip_bytes) {
+					/* unexpected underrun! (cancelled?) */
+					async->events |= COMEDI_CB_OVERFLOW;
+					goto underrun;
+				}
+			}
+			/* output the last scan */
+			for (i = 0; i < cmd->scan_end_arg; i++) {
+				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
+
+				if (comedi_buf_read_samples(s,
+							    &devpriv->
+							     ao_loopbacks[chan],
+							    1) == 0) {
+					/* unexpected underrun! (cancelled?) */
+					async->events |= COMEDI_CB_OVERFLOW;
+					goto underrun;
+				}
+			}
+			/* advance time of last scan */
+			devpriv->ao_last_scan_time +=
+				(u64)scans_avail * devpriv->ao_scan_period;
+		}
+	}
+	if (cmd->stop_src == TRIG_COUNT && async->scans_done >= cmd->stop_arg) {
+		async->events |= COMEDI_CB_EOA;
+	} else if (scans_avail < scans_since) {
+		async->events |= COMEDI_CB_OVERFLOW;
+	} else {
+		unsigned int time_inc = devpriv->ao_last_scan_time +
+					devpriv->ao_scan_period - now;
+
+		mod_timer(&devpriv->ao_timer,
+			  jiffies + usecs_to_jiffies(time_inc));
+	}
+
+underrun:
+	comedi_handle_events(dev, s);
+}
+
+static int waveform_ao_inttrig_start(struct comedi_device *dev,
+				     struct comedi_subdevice *s,
+				     unsigned int trig_num)
+{
+	struct waveform_private *devpriv = dev->private;
+	struct comedi_async *async = s->async;
+	struct comedi_cmd *cmd = &async->cmd;
+
+	if (trig_num != cmd->start_arg)
+		return -EINVAL;
+
+	async->inttrig = NULL;
+
+	devpriv->ao_last_scan_time = ktime_to_us(ktime_get());
+	devpriv->ao_timer.expires =
+		jiffies + usecs_to_jiffies(devpriv->ao_scan_period);
+
+	/* mark command as active */
+	smp_mb__before_atomic();
+	set_bit(WAVEFORM_AO_RUNNING, &devpriv->state_bits);
+	smp_mb__after_atomic();
+	add_timer(&devpriv->ao_timer);
+
+	return 1;
+}
+
+static int waveform_ao_cmdtest(struct comedi_device *dev,
+			       struct comedi_subdevice *s,
+			       struct comedi_cmd *cmd)
+{
+	int err = 0;
+	unsigned int arg;
+
+	/* Step 1 : check if triggers are trivially valid */
+
+	err |= comedi_check_trigger_src(&cmd->start_src, TRIG_INT);
+	err |= comedi_check_trigger_src(&cmd->scan_begin_src, TRIG_TIMER);
+	err |= comedi_check_trigger_src(&cmd->convert_src, TRIG_NOW);
+	err |= comedi_check_trigger_src(&cmd->scan_end_src, TRIG_COUNT);
+	err |= comedi_check_trigger_src(&cmd->stop_src, TRIG_COUNT | TRIG_NONE);
+
+	if (err)
+		return 1;
+
+	/* Step 2a : make sure trigger sources are unique */
+
+	err |= comedi_check_trigger_is_unique(cmd->stop_src);
+
+	/* Step 2b : and mutually compatible */
+
+	if (err)
+		return 2;
+
+	/* Step 3: check if arguments are trivially valid */
+
+	err |= comedi_check_trigger_arg_min(&cmd->scan_begin_arg,
+					    NSEC_PER_USEC);
+	err |= comedi_check_trigger_arg_is(&cmd->convert_arg, 0);
+	err |= comedi_check_trigger_arg_min(&cmd->chanlist_len, 1);
+	err |= comedi_check_trigger_arg_is(&cmd->scan_end_arg,
+					   cmd->chanlist_len);
+	if (cmd->stop_src == TRIG_COUNT)
+		err |= comedi_check_trigger_arg_min(&cmd->stop_arg, 1);
+	else	/* cmd->stop_src == TRIG_NONE */
+		err |= comedi_check_trigger_arg_is(&cmd->stop_arg, 0);
+
+	if (err)
+		return 3;
+
+	/* step 4: fix up any arguments */
+
+	/* round scan_begin_arg to nearest microsecond */
+	arg = cmd->scan_begin_arg;
+	arg = min(arg, rounddown(UINT_MAX, (unsigned int)NSEC_PER_USEC));
+	arg = NSEC_PER_USEC * DIV_ROUND_CLOSEST(arg, NSEC_PER_USEC);
+	err |= comedi_check_trigger_arg_is(&cmd->scan_begin_arg, arg);
+
+	if (err)
+		return 4;
+
+	return 0;
+}
+
+static int waveform_ao_cmd(struct comedi_device *dev,
+			   struct comedi_subdevice *s)
+{
+	struct waveform_private *devpriv = dev->private;
+	struct comedi_cmd *cmd = &s->async->cmd;
+
+	if (cmd->flags & CMDF_PRIORITY) {
+		dev_err(dev->class_dev,
+			"commands at RT priority not supported in this driver\n");
+		return -1;
+	}
+
+	devpriv->ao_scan_period = cmd->scan_begin_arg / NSEC_PER_USEC;
+	s->async->inttrig = waveform_ao_inttrig_start;
+	return 0;
+}
+
+static int waveform_ao_cancel(struct comedi_device *dev,
+			      struct comedi_subdevice *s)
+{
+	struct waveform_private *devpriv = dev->private;
+
+	s->async->inttrig = NULL;
+	/* mark command as no longer active */
+	clear_bit(WAVEFORM_AO_RUNNING, &devpriv->state_bits);
+	smp_mb__after_atomic();
+	/* cannot call del_timer_sync() as may be called from timer routine */
+	del_timer(&devpriv->ao_timer);
+	return 0;
+}
+
 static int waveform_ao_insn_write(struct comedi_device *dev,
 				  struct comedi_subdevice *s,
 				  struct comedi_insn *insn, unsigned int *data)
@@ -475,18 +674,23 @@ static int waveform_attach(struct comedi_device *dev,
 	dev->write_subdev = s;
 	/* analog output subdevice (loopback) */
 	s->type = COMEDI_SUBD_AO;
-	s->subdev_flags = SDF_WRITABLE | SDF_GROUND;
+	s->subdev_flags = SDF_WRITABLE | SDF_GROUND | SDF_CMD_WRITE;
 	s->n_chan = N_CHANS;
 	s->maxdata = 0xffff;
 	s->range_table = &waveform_ai_ranges;
+	s->len_chanlist = s->n_chan;
 	s->insn_write = waveform_ao_insn_write;
 	s->insn_read = waveform_ai_insn_read;	/* do same as AI insn_read */
+	s->do_cmd = waveform_ao_cmd;
+	s->do_cmdtest = waveform_ao_cmdtest;
+	s->cancel = waveform_ao_cancel;
 
 	/* Our default loopback value is just a 0V flatline */
 	for (i = 0; i < s->n_chan; i++)
 		devpriv->ao_loopbacks[i] = s->maxdata / 2;
 
 	setup_timer(&devpriv->ai_timer, waveform_ai_timer, (unsigned long)dev);
+	setup_timer(&devpriv->ao_timer, waveform_ao_timer, (unsigned long)dev);
 
 	dev_info(dev->class_dev,
 		 "%s: %u microvolt, %u microsecond waveform attached\n",
@@ -500,8 +704,10 @@ static void waveform_detach(struct comedi_device *dev)
 {
 	struct waveform_private *devpriv = dev->private;
 
-	if (devpriv)
+	if (devpriv) {
 		del_timer_sync(&devpriv->ai_timer);
+		del_timer_sync(&devpriv->ao_timer);
+	}
 }
 
 static struct comedi_driver waveform_driver = {