staging: comedi: comedi_test: move modulo operations for waveform

The fake waveform generator functions, `fake_sawtooth()` and
`fake_squarewave()`, called from `fake_waveform()`, have a
`current_time` parameter which is the time since the start of a waveform
period.  The parameter value may be greater than the waveform period so
they do a modulo operation to bring it into range.  Do the modulo
operations outside the functions in `waveform_ai_interrupt()` so that
the waveform generator functions always get a `current_time` parameter
less than the waveform period and do not have to do the modulo operation
themselves.  Also, only do the modulo operations when the time since the
start of a waveform exceeds the waveform period.  Usually, several
samples are produced in each waveform period and modulo operations are
typically more expensive than a simple comparison.

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>

diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
index cc35bd645d1b0908caf6b7d327649b69b7eafdb4..021522882905c64bfa4504d1d0d0cd3344a526b9 100644 (file)
--- a/drivers/staging/comedi/drivers/comedi_test.c
+++ b/drivers/staging/comedi/drivers/comedi_test.c
@@ -97,7 +97,6 @@ static unsigned short fake_sawtooth(struct comedi_device *dev,
        binary_amplitude *= devpriv->uvolt_amplitude;
        do_div(binary_amplitude, krange->max - krange->min);
 
-       current_time %= devpriv->usec_period;
        value = current_time;
        value *= binary_amplitude * 2;
        do_div(value, devpriv->usec_period);
@@ -125,7 +124,6 @@ static unsigned short fake_squarewave(struct comedi_device *dev,
        const struct comedi_krange *krange =
            &s->range_table->range[range_index];
 
-       current_time %= devpriv->usec_period;
        value = s->maxdata;
        value *= devpriv->uvolt_amplitude;
        do_div(value, krange->max - krange->min);
@@ -206,20 +204,24 @@ static void waveform_ai_interrupt(unsigned long arg)
 
        num_scans = comedi_nscans_left(s, num_scans);
        for (i = 0; i < num_scans; i++) {
+               unsigned long scan_remain_period = devpriv->scan_period;
+
                for (j = 0; j < cmd->chanlist_len; j++) {
                        unsigned short sample;
 
+                       if (devpriv->usec_current >= devpriv->usec_period)
+                               devpriv->usec_current %= devpriv->usec_period;
                        sample = fake_waveform(dev, CR_CHAN(cmd->chanlist[j]),
                                               CR_RANGE(cmd->chanlist[j]),
-                                              devpriv->usec_current +
-                                                  i * devpriv->scan_period +
-                                                  j * devpriv->convert_period);
+                                              devpriv->usec_current);
                        comedi_buf_write_samples(s, &sample, 1);
+                       devpriv->usec_current += devpriv->convert_period;
+                       scan_remain_period -= devpriv->convert_period;
                }
+               devpriv->usec_current += scan_remain_period;
        }
-
-       devpriv->usec_current += elapsed_time;
-       devpriv->usec_current %= devpriv->usec_period;
+       if (devpriv->usec_current >= devpriv->usec_period)
+               devpriv->usec_current %= devpriv->usec_period;
 
        if (cmd->stop_src == TRIG_COUNT && async->scans_done >= cmd->stop_arg)
                async->events |= COMEDI_CB_EOA;