linux-kernel - [PATCH 2/6] staging: comedi: usbduxsigma: don't clobber ao

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Message-Id: <1437666422-25222-3-git-send-email-abbotti@mev.co.uk>
Date:	Thu, 23 Jul 2015 16:46:58 +0100
From:	Ian Abbott <abbotti@....co.uk>
To:	<driverdev-devel@...uxdriverproject.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ian Abbott <abbotti@....co.uk>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	Bernd Porr <mail@...ndporr.me.uk>,
	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: [PATCH 2/6] 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@....co.uk>
Cc: <stable@...r.kernel.org> # 3.19 onwards
---
 drivers/staging/comedi/drivers/usbduxsigma.c | 33 ++++++++++++----------------
 1 file changed, 14 insertions(+), 19 deletions(-)

diff --git a/drivers/staging/comedi/drivers/usbduxsigma.c b/drivers/staging/comedi/drivers/usbduxsigma.c
index 22517de..dc0b25a 100644
--- a/drivers/staging/comedi/drivers/usbduxsigma.c
+++ b/drivers/staging/comedi/drivers/usbduxsigma.c
@@ -912,25 +912,6 @@ 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;
 }

@@ -943,6 +924,20 @@ 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) {
-- 
2.1.4

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