netdev - Re: [regression] e1000e broke e1000 (was: Re: [ANNOUNCE] e1000 toe1000e migration of PCI Express devices)

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Message-ID: <20080408195949.GB28148@elte.hu>
Date:	Tue, 8 Apr 2008 21:59:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
Cc:	"Kok, Auke-jan H" <auke-jan.h.kok@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	NetDev <netdev@...r.kernel.org>,
	e1000-list <e1000-devel@...ts.sourceforge.net>,
	linux-pci maillist <linux-pci@...ey.karlin.mff.cuni.cz>,
	Jeff Garzik <jeff@...zik.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"Allan, Bruce W" <bruce.w.allan@...el.com>,
	Greg KH <greg@...ah.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [regression] e1000e broke e1000 (was: Re: [ANNOUNCE] e1000
	toe1000e migration of PCI Express devices)

* Brandeburg, Jesse <jesse.brandeburg@...el.com> wrote:

> your expectation is that e1000 once loaded on this device in a 
> previous kernel (2.6.24) so it should continue to work, right? [...]

correct.

> > the eth0 interface is not detected at all:
> >    http://redhat.com/~mingo/misc/dmesg.e1000.bad
> 
> if you're running a no module kernel, you'll need to set 
> CONFIG_E1000E=y for your device to be detected.

there should be no need for me to set something that the kernel can do 
itself as well ...

> If there is a more reasonable solution you can come up with I am 
> interested.

i think the solution is obvious and simple: if e1000 is built-in then 
e1000e should not be allowed to be a module. (i.e. it should either be 
built-in in which case it will handle the PCI IDs, or it should be 
disabled - in which case e1000 will handle them.)

that way e1000e can take over the PCI IDs but we'll never get a 
non-working system, which takes an hour for a kernel hacker to figure 
out. The failure was totally silent. eth0 didnt show up at all.

Btw., a sidenote: this is another generally annoying property of Linux: 
there's no easy and user-visible enumeration of PCI IDs (devices) that 
we _could_ support but dont enable for some reason. It is a royal PITA 
to track down when some driver decides to (silently) ignore a piece of 
hardware.

Having a seemingly dead piece of hardware component is one of the most 
frustrating user experiences possible - the first instinctive reaction 
is "did my hw break???". The kernel should proactively know about all 
inactive pieces of hardware and should have a one-stop-shop for users 
where they can reassure themselves which devices are not active and why.

	Ingo
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