linux-kernel - Re: [RFC] driver-core: Remove dummy 'platform

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Message-ID: <CAL_JsqJSSHMaR=NJ3XWscxz1dKtG1N18W6JNDNKY3r3vtf9AXQ@mail.gmail.com>
Date:	Wed, 23 Apr 2014 09:16:58 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Grant Likely <grant.likely@...aro.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [RFC] driver-core: Remove dummy 'platform_bus'

On Wed, Apr 23, 2014 at 9:05 AM, Grant Likely <grant.likely@...aro.org> wrote:
> On Mon, 21 Apr 2014 16:05:29 -0500, Rob Herring <robherring2@...il.com> wrote:
>> On Wed, Nov 21, 2012 at 8:44 AM, Grant Likely <grant.likely@...retlab.ca> wrote:
>> > The "platform_bus" (note: not platform_bus_type) only exists as an empty
>> > directory to put platform devices into. However, it really doesn't make
>> > sense to segregate all the platform devices into a sub directory when
>> > typically they are memory mapped devices that doen't go through any
>> > particular bus. Particularly on embedded type platforms the platform_bus
>> > directory doesn't add anything.
>> >
>> > However, this will probably just end up breaking some userspace that
>> > depends on the /sys/devices/platform/ path to be present (no matter how
>> > much we protest that userspace must not depend on paths in sysfs). So
>> > while I'm seriously proposing this change, it may just be unacceptable
>> > ABI breakage
>>
>> An old thread, but was there ever a conclusion to this? We now have a
>> mixture of using platform_bus as the parent or not on various ARM
>> platforms.
>
> We kind of concluded in the opposite direction. Instead of removing the
> /sys/device/platform directory, the drivers/of code should be changed to
> use it.
>
> The following patch is sufficient to have the same effect. It doesn't
> unify the OF and non-OF paths of platform device addition, but it gets
> them closer. I've been nervous about applying it because I'm concerned
> about userspace breakage, but maybe it just needs to be merged and we
> can quirk out systems that break.

Given that we've changed practically all device names in converting to
DT and I haven't heard of any complaints, we may be okay.

We also have some platforms (imx6 for example) setting the parent to
an soc device. I still need to understand why the soc device needs to
be the parent, but it is pointless platform variation in my book. It
would also change the paths when someone has the whim to add an soc
device.

Rob
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