linux-kernel - Re: RFC: (re-)binding the VFIO platform driver to a platform device

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Date:	Tue, 1 Oct 2013 14:17:16 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Kim Phillips <kim.phillips@...aro.org>
CC:	<linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<a.motakis@...tualopensystems.com>, Alexander Graf <agraf@...e.de>,
	Alex Williamson <alex.williamson@...hat.com>,
	<stuart.yoder@...escale.com>,
	Wood Scott-B07421 <B07421@...escale.com>,
	Sethi Varun-B16395 <B16395@...escale.com>,
	Bhushan Bharat-R65777 <R65777@...escale.com>,
	Peter Maydell <peter.maydell@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	<santosh.shukla@...aro.org>, <kvm@...r.kernel.org>
Subject: Re: RFC: (re-)binding the VFIO platform driver to a platform device

On Tue, 2013-10-01 at 14:15 -0500, Scott Wood wrote:
> On Tue, 2013-10-01 at 13:38 -0500, Kim Phillips wrote:
> > Hi,
> > 
> > Santosh and I are having a problem figuring out how to enable binding
> > (and re-binding) platform devices to a platform VFIO driver (see
> > Antonis' WIP: [1]) in an upstream-acceptable manner.
> > 
> > Binding platform drivers currently depends on a string match in the
> > device node's compatible entry.  On an arndale, one can currently
> > rebind the same device to the same driver like so:
> > 
> > echo 12ce0000.i2c > /sys/bus/platform/drivers/s3c-i2c/12ce0000.i2c/driver/unbind
> > echo 12ce0000.i2c > /sys/bus/platform/drivers/s3c-i2c/bind
> > 
> > And one can bind it to the vfio-dt driver, as Antonis instructs, by
> > appending a 'vfio-dt' string to the device tree compatible entry for
> > the device.  Then this would work:
> > 
> > echo 12ce0000.i2c > /sys/bus/platform/drivers/s3c-i2c/12ce0000.i2c/driver/unbind
> > echo 12ce0000.i2c > /sys/bus/platform/drivers/vfio-dt/bind
> > 
> > Consequently, the hack patch below [2] allows any platform device to be
> > bound to the vfio-dt driver, without making changes to the device
> > tree.  It's a hack because I don't see having any driver name specific
> > code in drivers/base/bus.c being upstream acceptable.
> 
> Modifying the device tree is the worse part of this.

I think I missed something.  How do you reconcile "without making
changes to the device tree" with "appending a 'vfio-dt' string to the
device tree compatible entry"?

-Scott



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