linux-kernel - Re: [PATCH v2 0/5] mfd: Fix platform device ids to avoid probe failure

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Message-ID: <20150323100718.GD3557@localhost>
Date:	Mon, 23 Mar 2015 11:07:18 +0100
From:	Johan Hovold <johan@...nel.org>
To:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:	Lee Jones <lee.jones@...aro.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Johan Hovold <johan@...nel.org>,
	Support Opensource <support.opensource@...semi.com>,
	Milo Kim <milo.kim@...com>,
	patches@...nsource.wolfsonmicro.com,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/5] mfd: Fix platform device ids to avoid probe
 failure

On Fri, Mar 20, 2015 at 08:23:18PM +0100, Bartlomiej Zolnierkiewicz wrote:

> Commit 6e3f62f0793e ("mfd: core: Fix platform-device id generation")
> changed the way platform device ids are generated from mfd id base and
> cell ids in mfd_add_device().  Unfortunately the change in question
> breaks mfd drivers which are using mfd_add_devices() with mfd id base
> equal to -1 and non-zero cell ids (used to distinguish cells with
> the same name field).  The result is that mfd core tries to register
> platform devices with the same name which obviously fails and leads
> to mfd device probe failure.

First of all, thanks for finding these. I obviously overlooked this
class of drivers when fixing the device-id generation.

> Changing mfd_add_devices() mfd id base from -1 to 0 and at the same
> time setting proper cell ids for all cells fixes the issue.

This is however not the right fix. Instead you should be using
PLATFORM_DEVID_AUTO and keep the non-zero cell-ids as is, as this will
allow more than one mfd-device to be registered without resorting to
hacks.

Have a look at wm831x, for example, which offsets the device id base if
a wm831x_num parameter is passed in platform data (non-dt) to allow more
than one device to be registered. Your patch would break this, and still
not provide any other way to have multiple devices in a system.

Your changes would also break da9052, which would no longer allow more
than one device to be registered, something which was already fixed once
by commit b3f6c73db732 ("mfd: da9052-core: Fix platform-device id
collision").

Thanks,
Johan
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