staging: comedi: usbduxsigma: don't clobber ao_timer in command test

`devpriv->ao_timer` is used while an asynchronous command is running on
the AO subdevice.  It also gets modified by the subdevice's `cmdtest`
handler for checking new asynchronous commands,
`usbduxsigma_ao_cmdtest()`, which is not correct as it's allowed to
check new commands while an old command is still running.  Fix it by
moving the code which sets up `devpriv->ao_timer` into the subdevice's
`cmd` handler, `usbduxsigma_ao_cmd()`.

Note that the removed code in `usbduxsigma_ao_cmdtest()` checked that
`devpriv->ao_timer` did not end up less that 1, but that could not
happen due because `cmd->scan_begin_arg` or `cmd->convert_arg` had
already been range-checked.

Also note that we tested the `high_speed` variable in the old code, but
that is currently always 0 and means that we always use "scan" timing
(`cmd->scan_begin_src == TRIG_TIMER` and `cmd->convert_src == TRIG_NOW`)
and never "convert" (individual sample) timing (`cmd->scan_begin_src ==
TRIG_FOLLOW` and `cmd->convert_src == TRIG_TIMER`).  The moved code
tests `cmd->convert_src` instead to decide whether "scan" or "convert"
timing is being used, although currently only "scan" timing is
supported.

Fixes: fb1ef622e7a3 ("staging: comedi: usbduxsigma: tidy up analog output command support")
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: Bernd Porr <mail@berndporr.me.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: <stable@vger.kernel.org> # 3.19 onwards
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/usbduxsigma.c b/drivers/staging/comedi/drivers/usbduxsigma.c
index 2d684747a639dc24cbdb59cb78248008fe4584b1..dcb7f3037dea82d2bad825cf324b8e8a04f5298c 100644 (file)
--- a/drivers/staging/comedi/drivers/usbduxsigma.c
+++ b/drivers/staging/comedi/drivers/usbduxsigma.c
@@ -914,25 +914,6 @@ static int usbduxsigma_ao_cmdtest(struct comedi_device *dev,
        if (err)
                return 3;
 
-       /* Step 4: fix up any arguments */
-
-       /* we count in timer steps */
-       if (high_speed) {
-               /* timing of the conversion itself: every 125 us */
-               devpriv->ao_timer = cmd->convert_arg / 125000;
-       } else {
-               /*
-                * timing of the scan: every 1ms
-                * we get all channels at once
-                */
-               devpriv->ao_timer = cmd->scan_begin_arg / 1000000;
-       }
-       if (devpriv->ao_timer < 1)
-               err |= -EINVAL;
-
-       if (err)
-               return 4;
-
        return 0;
 }
 
@@ -945,6 +926,20 @@ static int usbduxsigma_ao_cmd(struct comedi_device *dev,
 
        down(&devpriv->sem);
 
+       if (cmd->convert_src == TRIG_TIMER) {
+               /*
+                * timing of the conversion itself: every 125 us
+                * at high speed (not used yet)
+                */
+               devpriv->ao_timer = cmd->convert_arg / 125000;
+       } else {
+               /*
+                * timing of the scan: every 1ms
+                * we get all channels at once
+                */
+               devpriv->ao_timer = cmd->scan_begin_arg / 1000000;
+       }
+
        devpriv->ao_counter = devpriv->ao_timer;
 
        if (cmd->start_src == TRIG_NOW) {