linux-kernel - Re: [PATCH] Driver core: Don't ignore bus_attach

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Message-ID: <Pine.LNX.4.44L0.0610111036290.5690-100000@iolanthe.rowland.org>
Date:	Wed, 11 Oct 2006 10:49:36 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
cc:	Jaroslav Kysela <perex@...e.cz>, Andrew Morton <akpm@...l.org>,
	ALSA development <alsa-devel@...a-project.org>,
	Takashi Iwai <tiwai@...e.de>, Greg KH <gregkh@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Kosina <jikos@...os.cz>,
	Castet Matthieu <castet.matthieu@...e.fr>,
	Akinobu Mita <akinobu.mita@...il.com>
Subject: Re: [PATCH] Driver core: Don't ignore bus_attach_device() retval

On Mon, 9 Oct 2006, Cornelia Huck wrote:

> From: Cornelia Huck <cornelia.huck@...ibm.com>
> 
> Check for return value of bus_attach_device() in device_add(). Add a
> function bus_delete_device() that undos the effects of bus_add_device().
> bus_remove_device() now undos the effects of bus_attach_device() only.
> device_del() now calls bus_remove_device(), kobject_uevent(),
> bus_delete_device() which makes it symmetric to the call sequence in
> device_add().

You know, I'm not so sure device registration should fail when 
bus_attach_device() returns an error.

After all, the device really is there even if it's not working properly.  
In the Windows device manager it would show up with a big red X through 
it, but it _would_ show up.

Furthermore there are subtle problems that can arise.  In effect, the
device is registered for a brief time (while the driver is probed) and
then unregistered without giving the bus subsystem a chance to prepare for
the removal.  With USB this can lead to problems; if the driver called
usb_set_interface() then child devices would be created below the one
being probed -- and they would never get removed.

Has this question been raised before?  Is there any reason not to 
register a device even when probing fails?

In fact, we might want to separate driver probing from device_add()  
entirely.  That is, make them available as two separate function calls.  
That way the subsystem driver will have a chance to create attribute files
before a uevent is generated and a driver is loaded.  (That should help
udev to work better.)  This would require a larger change, though --
probably requiring an alternate version of device_add().

Alan Stern

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