linux-kernel - Re: [PATCH 1/3] PM: Introduce new top level suspend and hibernation callbacks (rev. 8)

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Date:	Sun, 13 Apr 2008 23:39:43 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	benh@...nel.crashing.org
Cc:	Greg KH <greg@...ah.com>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	David Brownell <david-b@...bell.net>,
	Pavel Machek <pavel@....cz>, Oliver Neukum <oliver@...kum.org>,
	Nigel Cunningham <ncunningham@...a.org.au>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/3] PM: Introduce new top level suspend and hibernation callbacks (rev. 8)

On Sunday, 13 of April 2008, Benjamin Herrenschmidt wrote:
> 
> On Sun, 2008-04-13 at 15:33 +0200, Rafael J. Wysocki wrote:
> > + *     The PM core executes @prepare() for all devices before starting to
> > + *     execute suspend callbacks for any of them, so drivers may assume all of
> > + *     the other devices to be present and functional while @prepare() is being
> > + *     executed.  In particular, it is safe to make GFP_KERNEL memory
> > + *     allocations from within @prepare().  However, drivers may NOT assume
> > + *     anything about the availability of the user space at that time and it
> > + *     is not correct to request firmware from within @prepare() (it's too
> > + *     late to do that).  [To work around this limitation, drivers may
> > + *     register suspend and hibernation notifiers that are executed before the
> > + *     freezing of tasks.]
> 
> Can you tell me why you kept that limitation with user space ?
> 
> I don't see the point... On the contrary, prepare() is the pefect place
> to implement handshaking with userspace for drivers that need to do so,
> such as the DRM.

This _comment_ reflects the current situation, which is that we freeze tasks
before a suspend.  When it's no longer necessary to do that, I'll be happy to
change this comment.  For now, however, that's not the case.

Thanks,
Rafael
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