linux-kernel - Re: [PATCH 13/15] USB: ehci: make orion and mxc bus glues coexist

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Message-ID: <Pine.LNX.4.44L0.1301221011190.1510-100000@iolanthe.rowland.org>
Date:	Tue, 22 Jan 2013 10:19:06 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Manjunath Goudar <manjunath.goudar@...aro.org>
cc:	Arnd Bergmann <arnd@...db.de>, <balbi@...com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <arm@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, Shawn Guo <shawn.guo@...aro.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	Gregory Clement <gregory.clement@...e-electrons.com>
Subject: Re: [PATCH 13/15] USB: ehci: make orion and mxc bus glues coexist

On Tue, 22 Jan 2013, Manjunath Goudar wrote:

> > >  I think we can actually
> > > get the same results by turning the Kconfig logic around and making
> > > the platform glue drivers 'select USB_EHCI_HCD' than depending on
> > > it.
> >
> > That's a good idea.  The Kconfig changes would have to be done
> > carefully to make sure that the dependency on USB_ARCH_HAS_EHCI still
> > applies to all the platform drivers.
> >
> > Manjunath, would you like to send a patch to do this?
> >
> > Alan Stern
> >
> > Ya sure,could you explain little bit  briefly about the Kconfig changes.

Suppose you do exactly what Arnd proposed: add "select USB_EHCI_HCD" to
the Kconfig entries for each of the platform glue drivers.  Then
consider what would happen in a build where USB_ARCH_HAS_EHCI is "n"
but one of those glue drivers is enabled.  There would be conflicting
requirements on USB_EHCI_HCD: The new "select" would force it to be on,
but the existing "depends on USB && USB_ARCH_HAS_EHCI" would force it
to be off.  The build would fail.

In order to prevent this, you have to make sure that each glue driver
depends on USB_ARCH_HAS_EHCI.  A simple way to do this is to surround
the Kconfig entries for those drivers with "if USB && 
USB_ARCH_HAS_EHCI" ... "endif".

Come to think of it, the "if USB" part really should protect the entire 
file.

Alan Stern

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