linux-kernel - Re: [PATCH 1/6] staging: comedi: usbduxsigma: don't clobber ai

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Date:	Fri, 24 Jul 2015 17:57:37 +0100
From:	Bernd Porr <mail@...ndporr.me.uk>
To:	Ian Abbott <abbotti@....co.uk>
CC:	driverdev-devel@...uxdriverproject.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/6] staging: comedi: usbduxsigma: don't clobber ai_timer
 in command test

Reviewed-by: Bernd Porr <mail@...ndporr.me.uk>

Ian Abbott wrote:
> `devpriv->ai_timer` is used while an asynchronous command is running on
> the AI subdevice.  It also gets modified by the subdevice's `cmdtest`
> handler for checking new asynchronous commands
> (`usbduxsigma_ai_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->ai_timer` and
> `devpriv->ai_interval` into the subdevice's `cmd` handler,
> `usbduxsigma_ai_cmd()`.
> 
> Note that the removed code in `usbduxsigma_ai_cmdtest()` checked that
> `devpriv->ai_timer` did not end up less than than 1, but that could not
> happen because `cmd->scan_begin_arg` had already been checked to be at
> least the minimum required value (at least when `cmd->scan_begin_src ==
> TRIG_TIMER`, which had also been checked to be the case).
> 
> Fixes: b986be8527c7 ("staging: comedi: usbduxsigma: tidy up analog input command support)
> Signed-off-by: Ian Abbott <abbotti@....co.uk>
> Cc: <stable@...r.kernel.org> # 3.19 onwards
> ---
>  drivers/staging/comedi/drivers/usbduxsigma.c | 37 ++++++++++++----------------
>  1 file changed, 16 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/staging/comedi/drivers/usbduxsigma.c b/drivers/staging/comedi/drivers/usbduxsigma.c
> index eaa9add..22517de 100644
> --- a/drivers/staging/comedi/drivers/usbduxsigma.c
> +++ b/drivers/staging/comedi/drivers/usbduxsigma.c
> @@ -550,27 +550,6 @@ static int usbduxsigma_ai_cmdtest(struct comedi_device *dev,
>  	if (err)
>  		return 3;
>  
> -	/* Step 4: fix up any arguments */
> -
> -	if (high_speed) {
> -		/*
> -		 * every 2 channels get a time window of 125us. Thus, if we
> -		 * sample all 16 channels we need 1ms. If we sample only one
> -		 * channel we need only 125us
> -		 */
> -		devpriv->ai_interval = interval;
> -		devpriv->ai_timer = cmd->scan_begin_arg / (125000 * interval);
> -	} else {
> -		/* interval always 1ms */
> -		devpriv->ai_interval = 1;
> -		devpriv->ai_timer = cmd->scan_begin_arg / 1000000;
> -	}
> -	if (devpriv->ai_timer < 1)
> -		err |= -EINVAL;
> -
> -	if (err)
> -		return 4;
> -
>  	return 0;
>  }
>  
> @@ -668,6 +647,22 @@ static int usbduxsigma_ai_cmd(struct comedi_device *dev,
>  
>  	down(&devpriv->sem);
>  
> +	if (devpriv->high_speed) {
> +		/*
> +		 * every 2 channels get a time window of 125us. Thus, if we
> +		 * sample all 16 channels we need 1ms. If we sample only one
> +		 * channel we need only 125us
> +		 */
> +		unsigned int interval = usbduxsigma_chans_to_interval(len);
> +
> +		devpriv->ai_interval = interval;
> +		devpriv->ai_timer = cmd->scan_begin_arg / (125000 * interval);
> +	} else {
> +		/* interval always 1ms */
> +		devpriv->ai_interval = 1;
> +		devpriv->ai_timer = cmd->scan_begin_arg / 1000000;
> +	}
> +
>  	for (i = 0; i < len; i++) {
>  		unsigned int chan  = CR_CHAN(cmd->chanlist[i]);
>  

-- 
http://www.berndporr.me.uk
http://www.linux-usb-daq.co.uk
http://www.imdb.com/name/nm3293421/
+44 (0)7840 340069
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