linux-kernel - Re: [RESEND][PATCH] Bluetooth: Make request workqueue freezable

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Date:	Tue, 19 May 2015 10:26:46 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Takashi Iwai <tiwai@...e.de>
cc:	Laura Abbott <labbott@...hat.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	Laura Abbott <labbott@...oraproject.org>,
	"Gustavo F. Padovan" <gustavo@...ovan.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	"bluez mailin list (linux-bluetooth@...r.kernel.org)" 
	<linux-bluetooth@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ming Lei <ming.lei@...onical.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	<linux-usb@...r.kernel.org>
Subject: Re: [RESEND][PATCH] Bluetooth: Make request workqueue freezable

On Tue, 19 May 2015, Takashi Iwai wrote:

> > > I am not convinced. Now we are hacking the Bluetooth core layer
> > > (which has nothing to do with the drivers suspend/resume or
> > > probe) to do something different so that we do not see this
> > > warning.
> > >
> > > I can not do anything about the platform in question choosing a
> > > unplug/replug for suspend/resume instead of having a proper USB
> > > suspend and resume handling. That is pretty much out of our
> > > control.

Actually one can do something about this.  I mean, one _can_ implement
proper USB suspend and resume handling in the Bluetooth driver.  At
this point the details aren't clear to me, but perhaps if the driver in
question had a reset_resume callback then it might work better.

> > >  I would rather have the USB subsystem delay the probe()
> > > callback if we tell it to.

This is possible.  I am not sure it would be the right thing to do,
though.  What happens if the probe routine gets called early on during
the boot-up procedure, before userspace is up and running?  The same
thing should happen here.

> > >  Of just have request_firmware()
> > > actually sleep until userspace is ready. Seriously, why is
> > > request_firmware not just sleeping for us.

It won't work.  The request_firmware call is part of the probe 
sequence, which in turn is part of the resume sequence.  Userspace 
doesn't start running again until the resume sequence is finished.  If 
request_firmware waited for userspace, it would hang.

Alan Stern

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