linux-kernel - Re: [PATCH] add function spin_event

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Date:	Mon, 09 Mar 2009 13:47:50 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Timur Tabi <timur@...escale.com>
CC:	Roland Dreier <rdreier@...co.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] add function spin_event_timeout()

Timur Tabi wrote:
> On Fri, Mar 6, 2009 at 7:11 PM, Roland Dreier <rdreier@...co.com> wrote:
>   
>>  > The function spin_event_timeout() takes a condition and timeout value
>>  > (in jiffies) as parameters.  It spins until either the condition is true
>>  > or the timeout expires.  It returns non-zero if the condition is true,
>>  > zero otherwise.
>>
>> What's the motivation for this?  Where do you plan to use it?
>>     
>
> I expect it would be useful for drivers that need to wait until a
> specific register has changed its value, but don't want to risk an
> infinite loop if the hardware is not functioning.  For example, to
> replace the while loop and subsequent check in this code:
>   

A jiffy is a really long time to be spinning, let alone liffies plural.  
In this use case are you expecting that the loop will iterate a very 
small number of times before returning, and the timeout case is a very 
unlikely error condition?

    J
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