linux-kernel - Re: RFC: Platform data for onboard USB assets

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Date:	Fri, 11 Mar 2011 16:39:39 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	andy.green@...aro.org
Cc:	Andy Green <andy@...mcat.com>,
	Linux USB list <linux-usb@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: RFC: Platform data for onboard USB assets

On Fri, Mar 11, 2011 at 3:47 PM, Andy Green <andy@...mcat.com> wrote:
> On 03/11/2011 10:45 PM, Somebody in the thread at some point said:
>>
>> On Fri, Mar 11, 2011 at 2:50 AM, Andy Green<andy@...mcat.com>  wrote:
>>>
>>> Hi -
>>>
>>> platform_data is a well established way in Linux to pass configuration
>>> data
>>> up to on-board assets from a machine file like mach-xyz.c.  It's also
>>> supported to pass platform_data up to devices that are probed
>>> asynchronously
>>> from busses like i2c as well, which is very handy.
>>>
>>> However AFAIK it's not possible to bind platform_data to probed USB
>>> devices
>>> as it stands.
>>
>> Oh, please no.
>>
>> platform_data is an ugly non-type-checked anonymous pointer.  If you
>> need to pass data to a driver, use something better designed.  A
>> device tree fragment would work, or provide some kind of query api.
>> platform_data is definitely the wrong approach.
>
> $ grep platform_data drivers/* -R | wc -l
> 2110

I'm not disputing that it is widely used; and it does make a certain
amount of sense for static device registrations, but it is not a nice
interface, and it is a horrible idea for dynamic devices.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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