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Commit b7e2a040 authored by Bernd Porr's avatar Bernd Porr Committed by Greg Kroah-Hartman
Browse files

staging: comedi: usbduxfast: usbduxfast_ai_cmdtest rounding error 



commit 5618332e5b955b4bff06d0b88146b971c8dd7b32 upstream.

The userspace comedilib function 'get_cmd_generic_timed' fills
the cmd structure with an informed guess and then calls the
function 'usbduxfast_ai_cmdtest' in this driver repeatedly while
'usbduxfast_ai_cmdtest' is modifying the cmd struct until it
no longer changes. However, because of rounding errors this never
converged because 'steps = (cmd->convert_arg * 30) / 1000' and then
back to 'cmd->convert_arg = (steps * 1000) / 30' won't be the same
because of rounding errors. 'Steps' should only be converted back to
the 'convert_arg' if 'steps' has actually been modified. In addition
the case of steps being 0 wasn't checked which is also now done.

Signed-off-by: default avatarBernd Porr <mail@berndporr.me.uk>
Cc: <stable@vger.kernel.org> # 4.4+
Reviewed-by: default avatarIan Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20191118230759.1727-1-mail@berndporr.me.uk


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 4101916e

drivers/staging/comedi/drivers/usbduxfast.c

+14 −7
Original line number Original line Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0+

// SPDX-License-Identifier: GPL-2.0+

/*

/*

 *  Copyright (C) 2004-2014 Bernd Porr, mail@berndporr.me.uk

 *  Copyright (C) 2004-2019 Bernd Porr, mail@berndporr.me.uk

 */

 */





/*

/*
@@ -8,7 +8,7 @@ 
 * Description: University of Stirling USB DAQ & INCITE Technology Limited

 * Description: University of Stirling USB DAQ & INCITE Technology Limited

 * Devices: [ITL] USB-DUX-FAST (usbduxfast)

 * Devices: [ITL] USB-DUX-FAST (usbduxfast)

 * Author: Bernd Porr <mail@berndporr.me.uk>

 * Author: Bernd Porr <mail@berndporr.me.uk>

 * Updated: 10 Oct 2014

 * Updated: 16 Nov 2019

 * Status: stable

 * Status: stable

 */

 */
@@ -22,6 +22,7 @@ 
 *

 *

 *

 *

 * Revision history:

 * Revision history:

 * 1.0: Fixed a rounding error in usbduxfast_ai_cmdtest

 * 0.9: Dropping the first data packet which seems to be from the last transfer.

 * 0.9: Dropping the first data packet which seems to be from the last transfer.

 *      Buffer overflows in the FX2 are handed over to comedi.

 *      Buffer overflows in the FX2 are handed over to comedi.

 * 0.92: Dropping now 4 packets. The quad buffer has to be emptied.

 * 0.92: Dropping now 4 packets. The quad buffer has to be emptied.
@@ -350,6 +351,7 @@ static int usbduxfast_ai_cmdtest(struct comedi_device *dev, 
				 struct comedi_cmd *cmd)

				 struct comedi_cmd *cmd)

{

{

	int err = 0;

	int err = 0;

	int err2 = 0;

	unsigned int steps;

	unsigned int steps;

	unsigned int arg;

	unsigned int arg;
@@ -399,11 +401,16 @@ static int usbduxfast_ai_cmdtest(struct comedi_device *dev, 
	 */

	 */

	steps = (cmd->convert_arg * 30) / 1000;

	steps = (cmd->convert_arg * 30) / 1000;

	if (cmd->chanlist_len !=  1)

	if (cmd->chanlist_len !=  1)

		err |= comedi_check_trigger_arg_min(&steps,

		err2 |= comedi_check_trigger_arg_min(&steps,

						     MIN_SAMPLING_PERIOD);

						     MIN_SAMPLING_PERIOD);

	err |= comedi_check_trigger_arg_max(&steps, MAX_SAMPLING_PERIOD);

	else

		err2 |= comedi_check_trigger_arg_min(&steps, 1);

	err2 |= comedi_check_trigger_arg_max(&steps, MAX_SAMPLING_PERIOD);

	if (err2) {

		err |= err2;

		arg = (steps * 1000) / 30;

		arg = (steps * 1000) / 30;

		err |= comedi_check_trigger_arg_is(&cmd->convert_arg, arg);

		err |= comedi_check_trigger_arg_is(&cmd->convert_arg, arg);

	}





	if (cmd->stop_src == TRIG_COUNT)

	if (cmd->stop_src == TRIG_COUNT)

		err |= comedi_check_trigger_arg_min(&cmd->stop_arg, 1);

		err |= comedi_check_trigger_arg_min(&cmd->stop_arg, 1);