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

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Date:	Tue, 1 Oct 2013 17:01:23 -0500
From:	Kim Phillips <kim.phillips@...aro.org>
To:	scottwood@...escale.com
Cc:	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	a.motakis@...tualopensystems.com, agraf@...e.de,
	alex.williamson@...hat.com, stuart.yoder@...escale.com,
	B07421@...escale.com, B16395@...escale.com, R65777@...escale.com,
	peter.maydell@...aro.org, 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, 1 Oct 2013 14:17:16 -0500
Scott Wood <scottwood@...escale.com> wrote:

> 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"?

one doesn't need to append 'vfio-dt' to the device tree compatibles if
one uses the hack that makes bind_store ignore trying to
driver_match_device() if the driver is 'vfio-dt'.

Kim
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