linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Date:	Tue, 01 Jun 2010 09:57:31 +0300
From:	Igor Stoppa <igor.stoppa@...ia.com>
To:	ext Arve Hjønnevåg <arve@...roid.com>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul@...p1.linux-foundation.org" <Paul@...p1.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	"Balbi Felipe (Nokia-D/Helsinki)" <felipe.balbi@...ia.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

Hi,

ext Arve Hjønnevåg wrote:

> It sounded like you were suggesting that initiating suspend from idle
> would somehow avoid the race condition with wakeup events. All I'm
> saying is that you would need to block suspend in all the same places.
> If you don't care about ignoring wakeup events, then sure you can
> initiate suspend from idle.
>   

Sorry if i'm asking something that was already said, but the thread is 
quite complex and i am not sure i have been able to grasp all of it.

So, regardless of the SW implementation:

-1) are you focusing on "good" HW or do you want to address all at the 
same time?

-2) would you be ok with addressing "bad" HW as a special case, which 
requires workarounds and shouldn't dictate the overall design?

-3) do you agree with the assumption that new HW is expected to get 
reasonably better and therefore workarounds at point 2) will 
progressively be confined to devices less and less common?

-4) going to the definition of "good" and "bad" (maybe this should have 
come earlier in the list), can we define "good" HW as HW where:
 * suspend state and lowest achievable runtime idle state are basically 
equivalent from both power consumption and latency pov
 * the HW itself is properly able to track wakeup sources while it is in 
its deepest power state (as example OMAP3 has few independent 
wake-capable pads and a "wake ring" where one only gets the information 
that at least one of the pads belonging to such ring has received a wakeup)
 * wakeup sources can be dynamically masked at HW level, so that if a 
peripheral is not interesting, it doesn't wakeup the system (for example 
the camera button when the camera cover is closed)

-5) HW that is not capable of properly generating asynchronous signal is 
most likely the cause for extra timers in kernel and it should be 
considered "bad" - in any other case having recurring in-kernel timers 
should be treated as bugs, if their existence is not tied to some 
meaningful work

thanks, igor
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