linux-kernel - Re: arm qemu test failures due to 'driver-core: platform: probe of-devices only using list of compatibles'

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Message-ID: <20160215162753.GI12289@pengutronix.de>
Date:	Mon, 15 Feb 2016 17:27:53 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Robin Murphy <robin.murphy@....com>,
	Guenter Roeck <linux@...ck-us.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: arm qemu test failures due to 'driver-core: platform: probe
 of-devices only using list of compatibles'

Hello Russell,

On Mon, Feb 15, 2016 at 02:43:44PM +0000, Russell King - ARM Linux wrote:
> On Mon, Feb 15, 2016 at 01:11:49PM +0000, Robin Murphy wrote:
> > FWIW the PL180 on my Juno still works fine with this patch picked on top of
> > -rc3, so the issue would seem to be something else - From a quick comparison
> > between the DTs I see a slight difference in compatible strings for the
> > clocks, but the more likely-looking suspect is that the VExpress DT
> > references some GPIOs where the Juno DT doesn't.
> 
> Maybe it would be a good idea that Uwe creates a patch which initially
> warns when a DT platform device falls back to matching via the platform
> strings?
> 
> It's likely that the "basic subsystem" platform drivers are silent when
> they probe, so having notification of a fallback would at least put
> something into the kernel log when that happens - and then later change
> that to be a hard failure (as Uwe is trying to do with his patch.)
> 
> However, I have to bring up another point: is what Uwe is trying to do
> actually the right thing?  The DT platform device code has the ability
> to create standard platform devices from DT, with an of_node, but with
> standard names, and platform data.  It's there for compatibility with
> older systems, and is there to allow systems to be transitioned over.
> 
> This patch breaks all that: despite the DT code changing the platform
> device bus_id from the address.nodename format to the standard format
> (thus allowing unconverted platform drivers to match), this patch
> means that because the platform device has a of_node attached, this
> will now fail.
> 
> Therefore, I think Uwe's patch is just wrong - or, if it's something we
> want, the auxdata table support code needs to _also_ be ripped out of
> the drivers/of/platform.c code, but that then means anyone who wants to
> go through the conversion has a big flag-day change to go through.

That's a valid concern I wasn't aware of when I created the patch.

So maybe just emitting a warning as you suggested is a good idea. And
additionally only emit it when the driver is dt aware, too.

Greg, can you drop this patch, or do you need a proper changelog for a
revert? On top of that I'd then create a new patch which is more
conservative.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |