linux-kernel - Re: [PATCH 1/1] driver core: disable device's runtime pm during shutdown

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Message-ID: <20111205085632.5976fe96@notabene.brown>
Date:	Mon, 5 Dec 2011 08:56:32 +1100
From:	NeilBrown <neilb@...e.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Greg KH <greg@...ah.com>, Peter Chen <peter.chen@...escale.com>,
	gregkh@...e.de, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, stern@...land.harvard.edu,
	hzpeterchen@...il.com, Igor Grinberg <grinberg@...pulab.co.il>
Subject: Re: [PATCH 1/1] driver core: disable device's runtime pm during
 shutdown

On Wed, 16 Nov 2011 00:16:08 +0100 "Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Tuesday, November 15, 2011, Greg KH wrote:
> > On Mon, Nov 14, 2011 at 11:27:37PM +0100, Rafael J. Wysocki wrote:
> > > On Monday, November 14, 2011, Peter Chen wrote:
> > > > There may be an issue when the user issue "reboot/shutdown" command, then
> > > > the device has shut down its hardware, after that, this runtime-pm featured
> > > > device's driver will probably be scheduled to do its suspend routine,
> > > > and at its suspend routine, it may access hardware, but the device has
> > > > already shutdown physically, then the system hang may be occurred.
> > > > 
> > > > I ran out this issue using an auto-suspend supported USB devices, like
> > > > 3G modem, keyboard. The usb runtime suspend routine may be scheduled
> > > > after the usb controller has been shut down, and the usb runtime suspend
> > > > routine will try to suspend its roothub(controller), it will access
> > > > register, then the system hang occurs as the controller is shutdown.
> > > > Signed-off-by: Peter Chen <peter.chen@...escale.com>
> > > 
> > > Greg, do you want me to take this one?
> > 
> > Please do:
> > 	Acked-by: Greg Kroah-Hartman <gregkh@...e.de>
> 
> Done, thanks!
> 

Hi,
 this patches causes a problem for me.

Specifically it makes it impossible to power-down a device which uses twl4030
for power control on an omap3 processor.

To perform the shutdown we need to send a command over the i2c bus.
The relevant bus is called omap_i2c.1 and this is normally in suspend mode.
When a request is sent, omap_i2c_xfer uses pm_runtime_get_sync to wake it up,
performs the transfer, then calls pm_runtime_put to let it go back to sleep.

So it is asleep when the new pm_runtime_disable() call is made, so it stays
asleep, omap_i2c_xfer cannot wake it, the transfer doesn't happen and the
system doesn't get powered off.

So here is a device that should *not* have pm disabled at shutdown.

So I feel this fix is a little too heavy-handed.
I don't fully understand the problem scenario described above but it seems to
me that if the auto-suspend timer can fire after the hardware has been shut
down, then maybe the hardware-shutdown should be disabling that timer.  Maybe?

Suggestions?

Thanks,
NeilBrown

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