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

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Date:	Fri, 24 Jul 2015 17:58:27 +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 2/6] staging: comedi: usbduxsigma: don't clobber ao_timer
 in command test

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

Ian Abbott wrote:
> `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) {

-- 
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