linux-kernel - Re: [PATCH] Staging: comedi: add timeouts to while loops in s626.c

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Date:	Mon, 3 Mar 2014 14:13:22 +0000
From:	Ian Abbott <abbotti@....co.uk>
To:	Chase Southwood <chase.southwood@...oo.com>,
	Ian Abbott <ian.abbott@....co.uk>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:	"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] Staging: comedi: add timeouts to while loops in s626.c

On 2014-03-02 04:13, Chase Southwood wrote:
>> On Friday, February 28, 2014 11:49 PM, Chase Southwood <chase.southwood@...oo.com> wrote:
>
>>> On Friday, February 28, 2014 11:26 AM, Ian Abbott <abbotti@....co.uk> wrote:
>>>> On 2014-02-28 07:35, Chase Southwood wrote:
>
> [snip]
>
>>> In the case of s626_send_dac(), it doesn't seem to be used in any
>>> critical sections, so it could make use of Hartley's comedi_timeout().
>>>
>>> Some of the timeout errors could be propagated, especially for
>>> s626_send_dac() which is only reachable from very few paths.
>>
>>
>> Awesome, I'll swap all of my timeouts out for comedi_timeout() in s626_send_dac().
>
> Actually, after taking another look at this, I don't think that using comedi_timeout()
> here is going to work, actually.
> The context from which s626_send_dac() is called allows sleep all right, but readl() isn't
> a comedi function and therefore it doesn't behave (in parameters or return values) as
> the callback function parameter to comedi_timeout() requires.  So unless I'm missing
> something particularly large here, I believe we'll have to do the timeouts here manually
> as well.  Am I correct here, and if so, would you like the iteration based timeouts here
> as well, or a sleep-based timeout similar to that employed by comedi_timeout()?

The readl() could be done in a small callback function.  As the 
different while loops are checking for different results from readl(), 
It would need a different callback functions for each case, or some 
creative use of the callback function's 'context' parameter.

-- 
-=( 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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