linux-kernel - Re: [PATCH v4] introduce macro spin_event

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Date:	Tue, 10 Mar 2009 11:11:27 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Will Newton <will.newton@...il.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org,
	rdreier@...co.com, jirislaby@...il.com, peterz@...radead.org,
	hancockrwd@...il.com, jeremy@...p.org
Subject: Re: [PATCH v4] introduce macro spin_event_timeout()

Will Newton wrote:

> The correct timescale is rather application dependant - for some
> accesses that cross clock domains it can be a requirement to wait for
> a small number of core clock cycles (2 - 20) for a condition to become
> true, for others, e.g. PIO, it is more appropriate to wait for a few
> 100 cycles.

The timeout is only needed to avoid hangs in the driver.  If the
response normally comes within 20 clocks, but you waited two
milliseconds until you gave up, that's not a bad thing.  At least after
two milliseconds you've aborted the loop and returned an error.

-- 
Timur Tabi
Linux kernel developer at Freescale
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