linux-kernel - Re: [PATCH] firewire: Fix ohci free

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Date:	Sat, 2 Feb 2013 16:30:30 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Mark Einon <mark.einon@...il.com>,
	Peter Hurley <peter@...leysoftware.com>,
	<linux1394-devel@...ts.sourceforge.net>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] firewire: Fix ohci free_irq() warning

On Feb 02 Alan Stern wrote:
> On Sat, 2 Feb 2013, Stefan Richter wrote:
> 
> > On Feb 01 Mark Einon wrote:
> > > On 1 February 2013 21:09, Peter Hurley <peter@...leysoftware.com> wrote:
> > > >>>> On Jan 29 Alan Stern wrote:
> > > >>>>> Why does the pci_suspend routine call free_irq() at all?  As far as I 
> > > >>>>> know, it's not supposed to do that.  Won't the device continue to use 
> > > >>>>> the same IRQ after it is resumed?
> > 
> > As far as I can tell, it happened to be done that way as a side effect of
> > how the probe() and resume() methods share code.  It has remained like
> > this since the initial implementation:
> > http://git.kernel.org/linus/2aef469a35a2
> 
> At one point, quite a few years ago, Linus complained about drivers the 
> release IRQs during suspend only to reacquire them during resume.  A 
> little refactoring should be able to separate out resource 
> acquisition/release (done only during probe and remove) from activation 
> and shutdown (also done during resume and suspend).
> 
> > Still, at this point I would like to learn whether .suspend() followed
> > by .remove() is a valid order of sequence which drivers must support
> > before I prepare myself to get comfortable with a refactoring of
> > firewire-ohci's .probe()/.resume()/suspend()/remove().  Obviously, so far
> > my assumption was that a successful .suspend() can only ever be followed
> > by .resume().
> 
> It depends on the subsystem.  Some subsystems do have suspend -> remove
> transitions and others don't.  In general, it's a good idea for drivers
> to be prepared for removal while the system is asleep.  Presumably any
> hot-unpluggable bus (which includes most of the important buses these
> days) would have to support it.

OK, thank you.  In this case we are of course dealing with the pci
subsystem (and with PCI/ CardBus/ PCI Express/ ExpressCard attached
hardware).  Maybe I should have addressed my question to linux-pci
instead of linux-pm; however, if this is the general expectation,
then I too prefer firewire-ohci to be able to handle it even if the pci
subsystem wouldn't require it presently (which now sounds unlikely).
-- 
Stefan Richter
-=====-===-= --=- ---=-
http://arcgraph.de/sr/
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