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

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Date:	Wed, 2 Oct 2013 13:32:38 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Yoder Stuart-B08248 <B08248@...escale.com>
CC:	Christoffer Dall <christoffer.dall@...aro.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Kim Phillips <kim.phillips@...aro.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"a.motakis@...tualopensystems.com" <a.motakis@...tualopensystems.com>,
	"agraf@...e.de" <agraf@...e.de>,
	Wood Scott-B07421 <B07421@...escale.com>,
	Sethi Varun-B16395 <B16395@...escale.com>,
	Bhushan Bharat-R65777 <R65777@...escale.com>,
	"peter.maydell@...aro.org" <peter.maydell@...aro.org>,
	"santosh.shukla@...aro.org" <santosh.shukla@...aro.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: RFC: (re-)binding the VFIO platform driver to a platform device

On Wed, 2013-10-02 at 13:25 -0500, Yoder Stuart-B08248 wrote:
> 
> > -----Original Message-----
> > From: Christoffer Dall [mailto:christoffer.dall@...aro.org]
> > Sent: Wednesday, October 02, 2013 10:14 AM
> > To: Alex Williamson
> > Cc: Kim Phillips; gregkh@...uxfoundation.org; linux-
> > kernel@...r.kernel.org; a.motakis@...tualopensystems.com; agraf@...e.de;
> > Yoder Stuart-B08248; Wood Scott-B07421; Sethi Varun-B16395; Bhushan
> > Bharat-R65777; peter.maydell@...aro.org; santosh.shukla@...aro.org;
> > kvm@...r.kernel.org
> > Subject: Re: RFC: (re-)binding the VFIO platform driver to a platform
> > device
> > 
> > Wouldn't a sysfs file to add compatibility strings to the vfio-platform
> > driver make driver_match_device return true and make everyone happy?
> 
> I had a similar thought.  Why can't we do something like:
> 
>   echo "fsl,i2c" > /sys/bus/platform/drivers/vfio-platform/new_compatible
>   echo 12ce0000.i2c > /sys/bus/platform/drivers/vfio-platform/bind
> 
> The first steps tell vfio-platform to register itself to handle
> "fsl,i2c" compatible devices.  The second step does the bind.

Needing to specify the compatible is hacky (we already know what device
we want to bind; why do we need to scrounge up more information than
that, and add a new sysfs interface for extending compatible matches,
and a more flexible data structure to back that up?), and is racy on
buses that can hotplug (which driver gets the new device?).

What's wrong with a non-vfio-specific flag that a driver can set, that
indicates that the driver is willing to try to bind to any device on the
bus if explicitly requested via the existing sysfs bind mechanism?

-Scott



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