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

[Scott Wood]

On Wed, 2013-10-02 at 13:25 -0500, Yoder Stuart-B08248 wrote:
> 
> > -----Original Message-----
> > From: Christoffer Dall [mailto:christoffer.dall@xxxxxxxxxx]
> > Sent: Wednesday, October 02, 2013 10:14 AM
> > To: Alex Williamson
> > Cc: Kim Phillips; gregkh@xxxxxxxxxxxxxxxxxxx; linux-
> > kernel@xxxxxxxxxxxxxxx; a.motakis@xxxxxxxxxxxxxxxxxxxxxx; agraf@xxxxxxx;
> > Yoder Stuart-B08248; Wood Scott-B07421; Sethi Varun-B16395; Bhushan
> > Bharat-R65777; peter.maydell@xxxxxxxxxx; santosh.shukla@xxxxxxxxxx;
> > kvm@xxxxxxxxxxxxxxx
> > 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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