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

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Date:	Tue, 25 Mar 2008 14:37:16 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Greg KH <greg@...ah.com>, 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>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC][PATCH] PM: Introduce new top level suspend and hibernation callbacks (rev. 3)

Am Dienstag, 25. März 2008 13:40:53 schrieb Rafael J. Wysocki:
> On Tuesday, 25 of March 2008, Oliver Neukum wrote:
> > Am Montag 24 März 2008 schrieb Rafael J. Wysocki:

> > > + *     after @prepare() returns.  If @prepare() detects a situation it cannot
> > > + *     handle (e.g. registration of a child already in progress), it may return
> > > + *     -EAGAIN, so that the PM core can execute it once again (e.g. after the
> > > + *     new child has been registered) to recover from the race condition. This
> > > + *     method is executed for all kinds of suspend transitions and is followed
> > > + *     by one of the suspend callbacks: @suspend(), @freeze(), or @poweroff().
> > 
> > This could be understood so that disconnect() cannot be called.
> 
> At what time exactly?

I see no locking that would would prevent disconnect() in the window between
prepare() and suspend()/...
  
> > > + *     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.  However, they may NOT assume anything about the availability
> > > + *     of the user space at that time.
> > 
> > Probably it should be mentioned that this is the time to allocate memory
> > if you have to.
> 
> Well, not exactly.  Afterwards you cannot use GFP_KERNEL allocations, but
> GFP_NOIO should still work, although for hibernation it's quite possible that
> they'll fail if substantial amounts of memory are requested.
> 
> > And it is too late to request firmware. 
> 
> Yes.

This is better documented explicitly.

	Regards
		Oliver

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