linux-kernel - Re: [BUGFIX] PM: Fix active child counting when disabled and forbidden

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Date:	Wed, 14 Nov 2012 11:05:56 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Huang Ying <ying.huang@...el.com>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [BUGFIX] PM: Fix active child counting when disabled and forbidden

On Thursday, November 08, 2012 12:07:54 PM Alan Stern wrote:
> On Thu, 8 Nov 2012, Rafael J. Wysocki wrote:

[...]

I'd like to revisit this for a while if you don't mind.

> Your revised patch does do the job, except for a few problems.  
> Namely, while local_pci_probe() and pci_device_remove() are running,
> the device _does_ have a driver.

Right.

> This means that local_pci_probe() should not call pm_runtime_get_sync(),
> for example.  Doing so would invoke the driver's runtime_resume routine
> before calling the driver's probe routine!
> 
> The USB subsystem solves this problem by carefully keeping track of the 
> state of the device-driver binding:
> 
> 	Originally the device is UNBOUND.
> 
> 	At the start of the subsystem's probe routine, the state
> 	changes to BINDING.
> 
> 	If the probe succeeds then it changes to BOUND; otherwise
> 	it goes back to UNBOUND.
> 
> 	At the start of the subsystem's remove routine, the state
> 	changes to UNBINDING.  At the end it goes to UNBOUND.
> 
> When the state is anything other than BOUND, the subsystem's runtime PM 
> routines act as though there is no driver.

Well, that wouldn't help PCI, because some drivers want to use the
pm_runtime_* stuff in their .probe() routines and actually expect it to
work. :-)

Perhaps we can introduce something like

pm_runtime_get[_put]_skip_callbacks()

that would treat the device as though it had the power.no_callbacks flag
set and use that around the driver's .probe() in the PCI core?

Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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