patch "staging: comedi: usbduxsigma: don't clobber ao_timer in command test" added to staging-testing

This is a note to let you know that I've just added the patch titled

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

to my staging git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-testing branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will be merged to the staging-next branch sometime soon, after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.

From: Ian Abbott <[email protected]>
Date: Thu, 23 Jul 2015 16:46:58 +0100
Subject: 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.

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

index 2d684747a639..dcb7f3037dea 100644
@@ -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) {

2.4.6