linux-kernel - Re: [patch 2.6.30-rc3] platform_bus: remove "which platform

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Date:	Tue, 28 Apr 2009 20:24:46 -0700
From:	Greg KH <greg@...ah.com>
To:	David Brownell <david-b@...bell.net>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [patch 2.6.30-rc3] platform_bus:  remove "which
	platform_data?" confusion

On Tue, Apr 28, 2009 at 02:28:07AM -0700, David Brownell wrote:
> No comment on the bugfix part of $SUBJECT patch?

Well, no, I'm assuming it is correct :)

Should I just revert the original change, if the fact that busses are
using the platform_data field?

> On Monday 27 April 2009, Greg KH wrote:
> > 
> > > Those patches seem to support what I think is a misguided
> > > notion:  that somehow device.platform_data might move into
> > > the platform_device.  The problem with that idea is that it's
> > > a general purpose hook, and is used by other busses to provide
> > > board-specific configuration data ... not just for platform_bus.
> > 
> > It is?  What other busses do this?
> 
> SPI and I2C come quickly to mind...
> 
> Basically, *any* bus that could ever be used on an embedded
> system may need platform_data to explain how each discrete
> chip has been wired up on that particular board.  Very few
> such busses can self-enumerate like PCI or USB.  And most of
> the chips sitting on such busses expect to interface to fairly
> random external hardware.
> 
> And come to think of it, I've seen cases with PCI and USB
> where board-specific config data is needed.  PCI doesn't
> always wrap it up in some ACPI bytecode, and sometimes USB
> devices use "transceiverless link" hookup, so the board
> can just hook up using a differential pair.
> 
> SDIO/MMC doesn't tend to need it though, even for SDIO
> WLAN or MMC/SD storage links (eMMC, CE-ATA, etc).
> 
> 
> > And why, can't they use their own bus private data pointers?
> 
> ENOPATCH.  ;)
> 
> Though ... since devices on *any* bus may need this, I
> don't much see the point of modifying every bus like that.

Fair enough, no objection from me.

thanks,

greg k-h
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