linux-kernel - Re: [PATCH] i2c: rk3x: Increase wait timeout to 1 second

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Message-ID: <20150504083312.GN25193@pengutronix.de>
Date:	Mon, 4 May 2015 10:33:12 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Wolfram Sang <wsa@...-dreams.de>, Addy Ke <addy.ke@...k-chips.com>,
	Max Schwarz <max.schwarz@...ine.de>,
	Heiko Stuebner <heiko@...ech.de>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-rockchip@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: rk3x: Increase wait timeout to 1 second

On Thu, Apr 30, 2015 at 02:44:07PM -0700, Doug Anderson wrote:
> While it's not sensible for an i2c command to _actually_ need more
> than 200ms to complete, let's increase the timeout anyway.  Why?  It
> turns out that if you've got a large number of printks going out to a
> serial console, interrupts on a CPU can be disabled for hundreds of
> milliseconds. That's not a great situation to be in to start with
> (maybe we should put a cap in vprintk_emit()) but it's pretty annoying
> to start seeing unexplained i2c timeouts.
> 
> A normal system shouldn't see i2c timeouts anyway, so increasing the
> timeout should help people debugging without hurting other people
> excessively.
Hmm, correct me if I'm wrong: You say that the following can happen:

	rk3x_i2c_xfer calls wait_event_timeout and blocks
	schedule ... disable_irqs ... xfer complete ... do some work ... enable_irqs
	control back to i2c driver after timeout elapsed
	wait_event_timeout returned 0

The documentation of wait_event_timeout tells:

 * Returns:
 * 0 if the @condition evaluated to %false after the @timeout elapsed,
 * 1 if the @condition evaluated to %true after the @timeout elapsed,
 * or the remaining jiffies (at least 1) if the @condition evaluated
 * to %true before the @timeout elapsed.

Where is the misunderstanding?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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