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

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Message-ID: <s5hk2w14x8b.wl-tiwai@suse.de>
Date:	Thu, 21 May 2015 20:11:16 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Marcel Holtmann <marcel@...tmann.org>,
	Laura Abbott <labbott@...hat.com>,
	Oliver Neukum <oneukum@...e.com>,
	Ming Lei <ming.lei@...onical.com>,
	"David S. Miller" <davem@...emloft.net>,
	Laura Abbott <labbott@...oraproject.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"Gustavo F. Padovan" <gustavo@...ovan.org>,
	"bluez mailin list (linux-bluetooth@...r.kernel.org)" 
	<linux-bluetooth@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RESEND][PATCH] Bluetooth: Make request workqueue freezable

At Thu, 21 May 2015 13:37:56 -0400 (EDT),
Alan Stern wrote:
> 
> On Thu, 21 May 2015, Takashi Iwai wrote:
> 
> > At Thu, 21 May 2015 11:26:17 -0400 (EDT),
> > Alan Stern wrote:
> > > 
> > > On Thu, 21 May 2015, Takashi Iwai wrote:
> > > 
> > > > At Thu, 21 May 2015 10:18:08 -0400 (EDT),
> > > > Alan Stern wrote:
> > > > > 
> > > > > On Thu, 21 May 2015, Takashi Iwai wrote:
> > > > > 
> > > > > > Then avoiding the failed firmware is no solution, indeed.
> > > > > > If it's a new probe, it should be never executed during resume.
> > > > > 
> > > > > Can you expand this comment?  What's wrong with probing during resume?
> > > > 
> > > > Well, if the probe requires the access to a user-space file, it can't
> > > > be done during resume.  That's the very problem we're seeing now.
> > > > The firmware loader can't help much alone if it's a new device
> > > > object.
> > > 
> > > But the same thing happens during early boot, if the driver is built 
> > > into the kernel.  When the probe occurs, userspace isn't up and running 
> > > yet, so the firmware loader can't do anything.
> > > 
> > > Why should probe during resume be any worse than probe during early 
> > > boot?
> > 
> > The early boot has initrd, so the files can be there.  But the resume
> > has no way to fetch the file except for cached data.
> 
> I suppose USB could delay re-probing until userspace is running again,
> if we knew when that was.  But it would be awkward and prone to races.  
> It also would leave a user-visible window of time during which the 
> device does not exist, which we want to avoid.  (This may not matter 
> for bluetooth, but it does matter for other kinds of devices.)

Right.

> I would prefer to solve this problem in a different way, if possible.

Well, we're back in square again :)

But, before going further the discussion in loop again, I'd like to
know which firmware file actually hits.  Is it a non-existing
firmware?  Or is it a firmware that should have been cached?  In the
latter case, why it isn't used?


Takashi
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