linux-kernel - Re: [PATCH v2] Staging: comedi: convert while loop to timeout in ni_mio

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Date:	Tue, 14 Jan 2014 11:45:57 -0800
From:	Joe Perches <joe@...ches.com>
To:	Chase Southwood <chase.southwood@...oo.com>
Cc:	gregkh@...uxfoundation.org, abbotti@....co.uk,
	hsweeten@...ionengravers.com, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Staging: comedi: convert while loop to timeout in
 ni_mio_common.c.

On Tue, 2014-01-14 at 13:38 -0600, Chase Southwood wrote:
> This patch to ni_mio_common.c changes a while loop to a timeout for
> loop, which is preferred.
> 
> Signed-off-by: Chase Southwood <chase.southwood@...oo.com>
> ---
> 
> I know Mr. Abbott mentioned that he wouldn't expect clean-up patches to have to deal with this sort of thing, but I thought I'd at least give the timeout thing a try.  Feel free to disregard this and take v1 of this patch instead if you would just like the simple clean-up.  That being said, I used 10000 iterations at the suggestion of Mr. Abbott, and a short delay as well.  Let me know if these values seem incorrect.  Also, at some (but not all) locations in this file that currently use timeouts, contain a check for i == timeout, with a call to either printk or comedi_error if the operation actually times out.  Would something like that be required here?
> 
> Sorry for all of the questions, but I'm sort of new around here and I'd like to help out with more than just clean-ups and this seemed like a good opportunity to at least try!
> 
> 2: Changed from simple clean-up to swapping a timeout in for a while loop.
> 
>  drivers/staging/comedi/drivers/ni_mio_common.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/comedi/drivers/ni_mio_common.c b/drivers/staging/comedi/drivers/ni_mio_common.c
> index 457b884..05cd5ed 100644
> --- a/drivers/staging/comedi/drivers/ni_mio_common.c
> +++ b/drivers/staging/comedi/drivers/ni_mio_common.c
> @@ -687,12 +687,19 @@ static void ni_clear_ai_fifo(struct comedi_device *dev)
>  {
>  	const struct ni_board_struct *board = comedi_board(dev);
>  	struct ni_private *devpriv = dev->private;
> +	static const int timeout = 10000;
> +	int i;
>  
>  	if (board->reg_type == ni_reg_6143) {
>  		/*  Flush the 6143 data FIFO */
>  		ni_writel(0x10, AIFIFO_Control_6143);	/*  Flush fifo */
>  		ni_writel(0x00, AIFIFO_Control_6143);	/*  Flush fifo */
> -		while (ni_readl(AIFIFO_Status_6143) & 0x10) ;	/*  Wait for complete */
> +		/*  Wait for complete */
> +		for (i = 0; i < timeout; i++) {
> +			if(!(ni_readl(AIFIFO_Status_6143) & 0x10))
> +				break;
> +			udelay(1);
> +		}

some sort of error message would be nice too

		if (i >= timeout)
			comedi_error(dev, "FIFO flush timeout");


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