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

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Message-ID: <53A8A917.8090706@gmail.com>
Date:	Tue, 24 Jun 2014 00:24:23 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Kevin Hilman <khilman@...aro.org>,
	Doug Anderson <dianders@...omium.org>
CC:	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@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: exynos5: Properly use the "noirq" variants of suspend/resume

On 24.06.2014 00:19, Kevin Hilman wrote:
> 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.

Thanks for clarifying this. This means that we should be fine with the
noirq variant then.

Best regards,
Tomasz
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