linux-kernel - Re: [RFC PATCH 1/4] PLATFORM: introduce structure to bind async platform data to a dev path name

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Message-Id: <201103131351.36078.rjw@sisk.pl>
Date:	Sun, 13 Mar 2011 13:51:35 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	andy.green@...aro.org
Cc:	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, patches@...aro.org
Subject: Re: [RFC PATCH 1/4] PLATFORM: introduce structure to bind async platform data to a dev path name

On Sunday, March 13, 2011, Andy Green wrote:
> On 03/13/2011 01:03 AM, Somebody in the thread at some point said:
> 
> >>> Using device paths for this purpose seems to be very fragile to me.  Isn't
> >>> there any better solution?
> >>
> >> Given that this targets board definition files which commonly do the
> >> platform_add_device for the USB bus controller synchronously, and
> >> the bus-connected devices it is aimed at are soldered on to the
> >> board connected to specific bus controllers, the bus paths are
> >> completely deterministic.
> >
> > No they are not.
> >
> > The physical layout is deterministic, but the bus number, and device
> > number, is not.  You are using the bus number here in this path, so that
> > is not going to work, sorry.
> 
> Okay.  This is not a PC we are talking about.
> 
> If the platform / board definition file is registering the USB hosts 
> synchronously at boot time, the driver is composed into the monolithic 
> kernel, there are no PCI busses or whatever on the SoC, the bus indexing 
> is totally deterministic.  This is extremely common in the platform / 
> SoC case and is the case the patchset is targeted at.  Even further, the 
> only time you'd use it is to reach a USB asset that is wired up the same 
> board permanently as well.
> 
> Anyway this seems moot by now.

However, if you add a new infrastructure like this, it should be at least
usable on systems that you description doesn't apply to.

Thanks,
Rafael
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