linux-kernel - Re: [PATCH] Driver Core: Add platform device arch data V2

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Date:	Fri, 5 Jun 2009 21:54:15 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	linux-kernel@...r.kernel.org, paul@...an.com,
	khilman@...prootsystems.com, gregkh@...e.de,
	stern@...land.harvard.edu, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH] Driver Core: Add platform device arch data V2

On Friday 05 June 2009, Magnus Damm wrote:
> On Wed, Jun 3, 2009 at 6:01 PM, Rafael J. Wysocki<rjw@...k.pl> wrote:
> > On Tuesday 02 June 2009, Magnus Damm wrote:
> >> If you guys dislike adding arch specific data to struct platform
> >> device then for SuperH we can just (mis)use the arch specific data in
> >> struct device instead. I'm afraid that solution wastes memory since
> >> the data will only be used for platform devices anyway. So I prefer
> >> adding arch specific data to struct platform_device instead of struct
> >> device if possible.
> >
> > BTW, what is the difference really?  You can always put
> > dev.platform_data = NULL for devices that don't have any platform data,
> > can't you?
> 
> So the convention is that dev.platform_data points to driver-specific
> data. It may or may not be required by the driver. The format of this
> data is driver specific and should be the same across architectures.
> 
> What I'm trying to add with struct pdev_archdata is a place for
> architecture specific data. This data is needed by architecture
> specific code (for example runtime PM), and since it's architecture
> specific it should _never_ be touched by device driver code. Exactly
> like struct dev_archdata but for platform devices.
> 
> Like I said, we _could_ use struct device for this purpose, but it
> sounds like suboptimal software design to me. Using struct device
> means that we put data where it doesn't belong. I'd like to add
> _platform_ _device_ _specific_ data, not data that should be present
> in all struct devices in the system but only used in some cases.

OK, that explains the idea.  Perhaps it's woth putting into the changelog?

Best,
Rafael
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