linux-kernel - Re: [PATCH v4] Staging: comedi: convert while loop to timeout in ni_mio

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Message-ID: <52D66325.3010003@mev.co.uk>
Date:	Wed, 15 Jan 2014 10:29:57 +0000
From:	Ian Abbott <abbotti@....co.uk>
To:	Greg KH <gregkh@...uxfoundation.org>,
	Chase Southwood <chase.southwood@...oo.com>
CC:	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	Ian Abbott <ian.abbott@....co.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] Staging: comedi: convert while loop to timeout in
 ni_mio_common.c

On 2014-01-15 03:58, Greg KH wrote:
> On Tue, Jan 14, 2014 at 06:23:05PM -0600, Chase Southwood wrote:
>> This patch for ni_mio_common.c changes out a while loop for a timeout,
>> which is preferred.
>>
>> Signed-off-by: Chase Southwood <chase.southwood@...oo.com>
>> ---
>>
>> OK, here's another go at it.  Hopefully everything looks more correct
>> this time.  Greg, I've followed the pattern you gave me, and I really
>> appreciate all of the tips!  As always, just let me know if there are
>> still things that need adjusting (especially length of timeout, udelay,
>> etc.).
>>
>> Thanks,
>> Chase Southwood
>>
>> 2: Changed from simple clean-up to swapping a timeout in for a while loop.
>>
>> 3: Removed extra counter variable, and added error checking.
>>
>> 4: No longer using counter variable, using jiffies instead.
>>
>>   drivers/staging/comedi/drivers/ni_mio_common.c | 11 ++++++++++-
>>   1 file changed, 10 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..882b249 100644
>> --- a/drivers/staging/comedi/drivers/ni_mio_common.c
>> +++ b/drivers/staging/comedi/drivers/ni_mio_common.c
>> @@ -687,12 +687,21 @@ 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;
>> +	unsigned long timeout;
>>
>>   	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 */
>> +		timeout = jiffies + msec_to_jiffies(100);
>> +		while (ni_readl(AIFIFO_Status_6143) & 0x10) {
>> +			if (time_after(jiffies, timeout)) {
>> +				comedi_error(dev, "FIFO flush timeout.");
>> +				break;
>> +			}
>> +			udelay(1);
>
> Sleep for at least 10, as I think that's the smallest time delay you can
> sleep for anyway (meaning it will be that long no matter what number you
> put there less than 10, depending on the hardware used of course.)

udelay() doesn't sleep (though it may get pre-empted) and I think you 
can use any value you like within reason (up to a few 1000 microseconds).

>
> Other than that, looks much better.
>
> thanks,
>
> greg k-h
>


-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-
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