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

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Date:	Sun, 4 Dec 2011 21:42:02 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	NeilBrown <neilb@...e.de>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Greg KH <greg@...ah.com>,
	Peter Chen <peter.chen@...escale.com>, <gregkh@...e.de>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	<hzpeterchen@...il.com>, Igor Grinberg <grinberg@...pulab.co.il>
Subject: Re: [PATCH 1/1] driver core: disable device's runtime pm during
 shutdown

On Mon, 5 Dec 2011, NeilBrown wrote:

> 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.

In other words, to perform the system shutdown you need to send a 
command over the i2c bus after the bus controller's shutdown routine 
has been called?

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

Or maybe it shouldn't be shut down at all.

> 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?

That's not robust.  The timer can be restarted, and there are other 
ways of initiating runtime PM besides the timer.

> Suggestions?

Can the shutdown routine for the i2c controller simply call
pm_runtime_enable()?

Alan Stern

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