linux-kernel - Re: [linux-pm] [PATCH 1/8] PM: Add suspend block api.

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Message-ID: <n2ud6200be21005041340x32141eaem328765be77223cdd@mail.gmail.com>
Date:	Tue, 4 May 2010 13:40:27 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	markgross@...gnar.org
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Len Brown <len.brown@...el.com>, linux-doc@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Tejun Heo <tj@...nel.org>, Magnus Damm <damm@...l.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [linux-pm] [PATCH 1/8] PM: Add suspend block api.

2010/5/3 mark gross <640e9920@...il.com>:
> On Fri, Apr 30, 2010 at 03:36:54PM -0700, Arve Hjønnevåg wrote:
...
>> +When the policy is "opportunisic", there is a special value, "on", that can be
>> +written to /sys/power/state. This will block the automatic sleep request, as if
>> +a suspend blocker was used by a device driver. This way the opportunistic
>> +suspend may be blocked by user space whithout switching back to the "forced"
>> +mode.
>
> You know things would be so much easier if the policy was a one-shot
> styled thing.  i.e. when enabled it does what it does, but upon resume
> the policy must be re-enabled by user mode to get the opportunistic
> behavior.  That way we don't need to grab the suspend blocker from the
> wake up irq handler all the way up to user mode as the example below
> calls out.  I suppose doing this would put a burden on the user mode code
> to keep track of if it has no pending blockers registered after a wake
> up from the suspend.  but that seems nicer to me than sprinkling
> overlapping blocker critical sections from the mettle up to user mode.
>
> Please consider making the policy a one shot API that needs to be
> re-enabled after resume by user mode.  That would remove my issue with
> the design.
>

Making it one shot does not change where kernel code needs to block
suspend, but it does force user space to poll trying to suspend while
suspend is blocked by a driver.

-- 
Arve Hjønnevåg
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