linux-kernel - Re: [PATCH 5] PM: Update comments describing device power management callbacks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 21 Nov 2011 23:33:07 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Randy Dunlap <rdunlap@...otime.net>
Subject: Re: [PATCH 5] PM: Update comments describing device power management callbacks

On Monday, November 21, 2011, Alan Stern wrote:
> On Mon, 21 Nov 2011, Rafael J. Wysocki wrote:
> 
> > > > I said "Analogous to @suspend()" instead.  I'm not sure why this is not
> > > > sufficient?
> > > 
> > > Because @suspend() is very different!  Its description basically says 
> > > to do three things:
> > > 
> > > 	Quiesce the device,
> > > 
> > > 	Put it into a low-power state,
> > > 
> > > 	And enable wakeup events.
> > 
> > No, it doesn't any more.  It's being changed by the proposed patch too. :-)
> 
> I must have missed reading that part.  Okay...  but it seems weird that
> none of the new descriptions says anything about changing the power
> state.  Shouldn't the description of @suspend say something like "For
> many platforms and subsystems, the device should be put in a low-power
> state"?

Hmm.  I'm not really sure, actually, because I'd recommend that subsystems
rather than drivers change power states of devices and this description
is targeted at driver writers mostly.

> > > @freeze() is supposed to do the first but not the second or third.  
> > > This makes it only 33% similar to @suspend().  :-)
> > > 
> > > Also, the description of @suspend() says nothing about having a
> > > consistent memory image.
> > 
> > Because that is irrelevant.  The state of the device after the resume
> > has to be consistent, regardless of whether the resume is from RAM or
> > from an on-disk image.
> 
> Sure, the device's state will be consistent.  But will the contents of
> memory image be consistent?  Not if the device was doing DMA writes
> during the time when the image was created.

Well, since .suspend() is also expected to stop DMA, that's rather moot.

Thanks,
Rafael
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/