linux-kernel - Re: [PATCH] Explicitly disable BT radio using rfkill interface on suspend

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Date:	Wed, 20 May 2009 14:31:27 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Mario Limonciello <mario_limonciello@...l.com>
cc:	Oliver Neukum <oliver@...kum.org>, <linux-usb@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Marcel Holtmann <marcel@...tmann.org>,
	<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Explicitly disable BT radio using rfkill interface on
 suspend

On Wed, 20 May 2009, Mario Limonciello wrote:

> Hi Alan:
> 
> Alan Stern wrote:
> > On Wed, 20 May 2009, Oliver Neukum wrote:
> >
> >   
> >
> > That's okay.  Inelegant, perhaps, but workable.  Besides, as we see 
> > below, the new rule would have to do more than the old rule.
> >
> >   
> I agree this is a rather inelegant solution. A  new rule would have to
> be added to hid2hci then.  It's much more preferable to be able to fix
> kernel space from mucking up the device.  Is there a way to mark a
> device to /not/ run reset-resume after S3?

	echo 0 >/sys/bus/usb/devices/.../power/persist

This will also prevent reset-resume after hibernation.

> > Does that create the same removal event?  If it does then you wouldd be
> > in an unfortunate state.  The script would have to check somehow
> > whether the removal was deliberate or spontaneous.
> >   
> Yes it does create the same removal event when you switch to HID mode. 
> I don't know of any way that you can calculate if the switch was
> intentional.

You can't.  Instead you have to arrange things so that when the
intentional change was made, it left behind a timestamp indicator.  If
that timestamp if present and not more than a few seconds in the past,
you know the change was intentional.

Alan Stern

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