linux-kernel - Re: [PATCH] i2c: exynos5: Properly use the "noirq" variants of suspend/resume

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Date:	Mon, 23 Jun 2014 15:19:11 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Tomasz Figa <tomasz.figa@...il.com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	naveen krishna <ch.naveen@...sung.com>,
	Jingoo Han <jg1.han@...sung.com>,
	Jean Delvare <jdelvare@...e.de>, Simon Glass <sjg@...gle.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Masanari Iida <standby24x7@...il.com>,
	Sachin Kamat <sachin.kamat@...aro.org>,
	"linux-i2c\@vger.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: exynos5: Properly use the "noirq" variants of suspend/resume

Doug Anderson <dianders@...omium.org> writes:

[...]

> On Fri, Jun 20, 2014 at 4:59 PM, Tomasz Figa <tomasz.figa@...il.com> wrote:
>>
>> I'm not sure noirq is going to work correctly, at least not with current
>> callbacks. I can see a call to clk_prepare_enable() there which needs to
>> acquire a mutex.
>
> Nice catch, thanks!  :)
>
> OK, looking at that now.  Interestingly this doesn't seem to cause us
> problems in our ChromeOS 3.8 tree.  I just tried enabling:
>   CONFIG_DEBUG_ATOMIC_SLEEP=y
>
> ...and confirmed that I got it on right:
>
> # zgrep -i atomic /proc/config.gz
> CONFIG_DEBUG_ATOMIC_SLEEP=y
>
> I can suspend/resume with no problems.  My bet is that it works fine because:
>
> * resume_noirq is not considered "atomic" in the sense enforced by
> CONFIG_DEBUG_ATOMIC_SLEEP (at least not in 3.8--I haven't tried on
> ToT)

The reason is because "noirq" in the suspend/resume path actually means
no *device* IRQs for that specific device.

It's often assumed that the "noirq" callbacks are called with *all*
interrupts disabled, but that's not the case.  Only the IRQs for that
specific device are disabled when its noirq callbacks run.

Kevin
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