linux-kernel - Re: [PATCH v7] Staging: comedi: convert while loop to timeout in ni_mio

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Message-ID: <1389894391.35761.YahooMailNeo@web164002.mail.gq1.yahoo.com>
Date:	Thu, 16 Jan 2014 09:46:31 -0800 (PST)
From:	Chase Southwood <chase.southwood@...oo.com>
To:	Ian Abbott <abbotti@....co.uk>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:	Ian Abbott <ian.abbott@....co.uk>,
	"hsweeten@...ionengravers.com" <hsweeten@...ionengravers.com>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7] Staging: comedi: convert while loop to timeout in ni_mio_common.c

>On Thursday, January 16, 2014 5:31 AM, Ian Abbott <abbotti@....co.uk> wrote:

>On 2014-01-15 19:22, 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>
>> ---
>>
>> Hartley,
>> I sincerely apologize for the obvious mistake, I thought I had built it
>> but clearly I made a mistake somewhere, as your observation is exactly
>> correct.  It is now fixed.
>>
>> 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.
>>
>> 5: udelay for 10u, instead of 1u.
>>
>> 6: Scrap udelay entirely, in favor of cpu_relax. Include asm/processor.h
>> in order to use cpu_relax.
>>
>> 7: Fix typo (msec vs msecs).
>>
>>   drivers/staging/comedi/drivers/ni_mio_common.c | 12 +++++++++++-
>>   1 file changed, 11 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..ab7a74c 100644
>> --- a/drivers/staging/comedi/drivers/ni_mio_common.c
>> +++ b/drivers/staging/comedi/drivers/ni_mio_common.c
>> @@ -55,6 +55,7 @@
>>   #include <linux/interrupt.h>
>>   #include <linux/sched.h>
>>   #include <linux/delay.h>
>> +#include <asm/processor.h>
>>   #include "8255.h"
>>   #include "mite.h"
>>   #include "comedi_fc.h"
>> @@ -687,12 +688,21 @@ 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 + msecs_to_jiffies(500);
>> +        while (ni_readl(AIFIFO_Status_6143) & 0x10) {
>> +            if (time_after(jiffies, timeout)) {
>> +                comedi_error(dev, "FIFO flush timeout.");
>> +                break;
>> +            }
>> +            cpu_relax();
>> +        }
>>       } else {
>>           devpriv->stc_writew(dev, 1, ADC_FIFO_Clear);
>>           if (board->reg_type == ni_reg_625x) {
>>

>Sorry this is your worst nightmare, Chase.  Your patch is great and has 
>been modified in all the ways various people have suggested, but I don't 
>think it is suitable.
>
>After examining the code, it turns out ni_clear_ai_fifo() is sometimes 
>called from an interrupt service routine and I don't think you can wait 
>for jiffies to change in that case.  I think we need to go back to your 
>PATCH v2 and fix up the checkpatch.pl warning that Greg mentioned.
>
>Sorry about that.
>
>-- 
>-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk>        )=-
>-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-

It's absolutely no problem.  I'll get v2 cleaned up and sent out right away!

Thanks,
Chase Southwood
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