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: <20160215144344.GF10826@n2100.arm.linux.org.uk>
Date:	Mon, 15 Feb 2016 14:43:44 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Robin Murphy <robin.murphy@....com>
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	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'

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.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
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