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

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Date:	Mon, 31 May 2010 16:21:09 -0500
From:	James Bottomley <James.Bottomley@...e.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	tytso@....edu, LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	felipe.balbi@...ia.com, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Mon, 2010-05-31 at 22:49 +0200, Thomas Gleixner wrote:
> On Sat, 29 May 2010, James Bottomley wrote:
> > The job of the kernel is to accommodate hardware as best it can ...
> > sometimes it might not be able to, but most of the time it does a pretty
> > good job.
> > 
> > The facts are that C states and S states are different and are entered
> > differently. 
> 
> That's an x86'ism which is going away. And that's really completely
> irrelevant for the mobile device space. Can we please stop trying to
> fix todays x86 based laptop problems? They are simply not fixable.

You're the one mentioning x86, not me.  I already explained that some
MSM hardware (the G1 for example) has lower power consumption in S3
(which I'm using as an ACPI shorthand for suspend to ram) than any
suspend from idle C state.  The fact that current x86 hardware has the
same problem may be true, but it's not entirely relevant.

> > For some omap hardware, the power consumption in the
> > lowest C state (with all the ancillary power control) is the same as S3,
> > that's fine, suspend from idle works as well as suspend to ram modulo
> > bad apps. For quite a lot of MSM hardware, the lowest C state power
> > consumption is quite a bit above S3.  It's not acceptable to tell those
> > people "tough, your battery runs out in 30 minutes because you bought
> > the wrong hardware".  We have to figure out how to get to S3 ... whether
> > this is from idle or some other mechanism is again a discussion point,
> > but not doing it is not an option.
> 
> If you'd have read the answers from Alan carefully, then you'd have
> noticed that even x86 hardware is getting to the point where OMAP is
> today. i.e. support of transparent suspend from idle. If that wouldn't
> happen then x86 would be simply unusable for mobile devices. It's that
> easy. And we really do _NOT_ care about the existing laptop hardware
> which does not provide that because it's a lost case. Not only due to
> the missing (or just disabled) wakeup sources, also due to the fact
> that you cannot do sensible power management by completely disabling
> clock and/or power of unused devices in the chipset. There is a damn
> good reason why the mobile space is _NOT_ x86 based at the moment.

So not at all interested in x86 at the moment.

For MSM hardware, it looks possible to unify the S and C states by doing
suspend to ram from idle but I'm not sure how much work that is.

James


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