* [PATCH] staging: comedi: usbduxsigma: usbduxfast_ai_cmdtest rounding error
@ 2019-11-18 17:21 Bernd Porr
2019-11-18 18:04 ` Ian Abbott
0 siblings, 1 reply; 2+ messages in thread
From: Bernd Porr @ 2019-11-18 17:21 UTC (permalink / raw)
To: gregkh; +Cc: abbotti, driverdev-devel
'get_cmd_generic_timed' fills the cmd structure with an informed
guess and then calls 'usbduxfast_ai_cmdtest' 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 addion
the case of steps being 0 wasn't checked which is also now done.
Signed-off-by: Bernd Porr <mail@berndporr.me.uk>
---
drivers/staging/comedi/drivers/usbduxfast.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/drivers/staging/comedi/drivers/usbduxfast.c b/drivers/staging/comedi/drivers/usbduxfast.c
index 04bc488385e6..4af012968cb6 100644
--- 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@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
* Devices: [ITL] USB-DUX-FAST (usbduxfast)
* Author: Bernd Porr <mail@berndporr.me.uk>
- * 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 comedi_device *dev,
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 comedi_device *dev,
*/
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);
--
2.17.1
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^ permalink raw reply related [flat|nested] 2+ messages in thread* Re: [PATCH] staging: comedi: usbduxsigma: usbduxfast_ai_cmdtest rounding error
2019-11-18 17:21 [PATCH] staging: comedi: usbduxsigma: usbduxfast_ai_cmdtest rounding error Bernd Porr
@ 2019-11-18 18:04 ` Ian Abbott
0 siblings, 0 replies; 2+ messages in thread
From: Ian Abbott @ 2019-11-18 18:04 UTC (permalink / raw)
To: Bernd Porr, gregkh; +Cc: driverdev-devel
On 18/11/2019 17:21, Bernd Porr wrote:
> 'get_cmd_generic_timed' fills the cmd structure with an informed
> guess and then calls 'usbduxfast_ai_cmdtest' 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 addion
> the case of steps being 0 wasn't checked which is also now done.
>
> Signed-off-by: Bernd Porr <mail@berndporr.me.uk>
The patch subject needs changing as it refers to usbduxsigma, and this
patch is for usbduxfast.
While we're at it, there is a typo in the patch description "addion" =>
"addition".
Also, make it clear that 'get_cmd_generic_timed' is the user-space
comedilib function 'comedi_get_cmd_generic_timed()'.
> ---
> drivers/staging/comedi/drivers/usbduxfast.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/staging/comedi/drivers/usbduxfast.c b/drivers/staging/comedi/drivers/usbduxfast.c
> index 04bc488385e6..4af012968cb6 100644
> --- 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@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
> * Devices: [ITL] USB-DUX-FAST (usbduxfast)
> * Author: Bernd Porr <mail@berndporr.me.uk>
> - * 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 comedi_device *dev,
> 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 comedi_device *dev,
> */
> 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);
>
The actual patch looks good. A 'Cc:' line for "stable" kernel versions
4.4 and later could be added:
Cc: <stable@vger.kernel.org> # 4.4+
Please mark the updated patch as '[PATCH v2]' in the subject. Thanks.
--
-=( Ian Abbott <abbotti@mev.co.uk> || Web: www.mev.co.uk )=-
-=( MEV Ltd. is a company registered in England & Wales. )=-
-=( Registered number: 02862268. Registered address: )=-
-=( 15 West Park Road, Bramhall, STOCKPORT, SK7 3JZ, UK. )=-
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2019-11-18 18:04 ` Ian Abbott
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