From: Bernd Porr <mail@xxxxxxxxxxxxxxx> 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: Bernd Porr <mail@xxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 4.4+ Reviewed-by: Ian Abbott <abbotti@xxxxxxxxx> Link: https://lore.kernel.org/r/20191118230759.1727-1-mail@xxxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/staging/comedi/drivers/usbduxfast.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-) --- a/drivers/staging/comedi/drivers/usbduxfast.c +++ b/drivers/staging/comedi/drivers/usbduxfast.c @@ -1,6 +1,6 @@ // SPDX-License-Identifier: GPL-2.0+ /* - * Copyright (C) 2004-2014 Bernd Porr, mail@xxxxxxxxxxxxxxx + * Copyright (C) 2004-2019 Bernd Porr, mail@xxxxxxxxxxxxxxx */ /* @@ -8,7 +8,7 @@ * Description: University of Stirling USB DAQ & INCITE Technology Limited * Devices: [ITL] USB-DUX-FAST (usbduxfast) * Author: Bernd Porr <mail@xxxxxxxxxxxxxxx> - * Updated: 10 Oct 2014 + * Updated: 16 Nov 2019 * Status: stable */ @@ -22,6 +22,7 @@ * * * 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. * Buffer overflows in the FX2 are handed over to comedi. * 0.92: Dropping now 4 packets. The quad buffer has to be emptied. @@ -350,6 +351,7 @@ static int usbduxfast_ai_cmdtest(struct struct comedi_cmd *cmd) { int err = 0; + int err2 = 0; unsigned int steps; unsigned int arg; @@ -399,11 +401,16 @@ static int usbduxfast_ai_cmdtest(struct */ steps = (cmd->convert_arg * 30) / 1000; if (cmd->chanlist_len != 1) - err |= comedi_check_trigger_arg_min(&steps, - MIN_SAMPLING_PERIOD); - err |= comedi_check_trigger_arg_max(&steps, MAX_SAMPLING_PERIOD); - arg = (steps * 1000) / 30; - err |= comedi_check_trigger_arg_is(&cmd->convert_arg, arg); + err2 |= comedi_check_trigger_arg_min(&steps, + MIN_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; + err |= comedi_check_trigger_arg_is(&cmd->convert_arg, arg); + } if (cmd->stop_src == TRIG_COUNT) err |= comedi_check_trigger_arg_min(&cmd->stop_arg, 1);
