[PATCH 4.1 027/102] staging: comedi: usbduxsigma: dont clobber ao_timer in command test

Greg Kroah-Hartman
2015-09-19T17:38:49Z

From: Ian Abbott <abbotti@mev.co.uk>

commit c04a1f17803e0d3eeada586ca34a6b436959bc20 upstream.

`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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/staging/comedi/drivers/usbduxsigma.c | 33 +++++++++++----------------
1 file changed, 14 insertions(+), 19 deletions(-)

--- a/drivers/staging/comedi/drivers/usbduxsigma.c
+++ b/drivers/staging/comedi/drivers/usbduxsigma.c
@@ -912,25 +912,6 @@ static int usbduxsigma_ao_cmdtest(struct
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;
}

@@ -943,6 +924,20 @@ static int usbduxsigma_ao_cmd(struct com

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) {