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

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Message-Id: <20131001170244.ff4fb81d9a7a09598c4c6247@linaro.org>
Date:	Tue, 1 Oct 2013 17:02:44 -0500
From:	Kim Phillips <kim.phillips@...aro.org>
To:	gregkh@...uxfoundation.org
Cc:	linux-kernel@...r.kernel.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 13:00:54 -0700
Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:

> On Tue, Oct 01, 2013 at 01:38:31PM -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.
> 
> You are correct.
> 
> What is wrong with just doing the above unbind/bind things through
> sysfs, that is what it is there for, right?

The bind fails because the compatible string in the device tree doesn't
match that of the VFIO platform driver, so driver_match_device always
returns false.

Kim
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