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

[Scott Wood <scottwood@freescale.com>]

On Thu, 2013-10-10 at 03:01 -0500, Bhushan Bharat-R65777 wrote:
> 
> > -----Original Message-----
> > From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org] On Behalf Of
> > Kim Phillips
> > Sent: Thursday, October 10, 2013 8:36 AM
> > To: Wood Scott-B07421
> > Cc: Yoder Stuart-B08248; Wood Scott-B07421; christoffer.dall@linaro.org;
> > alex.williamson@redhat.com; linux-kernel@vger.kernel.org;
> > a.motakis@virtualopensystems.com; agraf@suse.de; Sethi Varun-B16395; Bhushan
> > Bharat-R65777; peter.maydell@linaro.org; santosh.shukla@linaro.org;
> > kvm@vger.kernel.org; gregkh@linuxfoundation.org
> > Subject: Re: RFC: (re-)binding the VFIO platform driver to a platform device
> > 
> > On Wed, 9 Oct 2013 15:03:19 -0500
> > Scott Wood <scottwood@freescale.com> wrote:
> > 
> > > On Wed, 2013-10-09 at 14:44 -0500, Yoder Stuart-B08248 wrote:
> > > > > From: Wood Scott-B07421
> > > > > Sent: Wednesday, October 09, 2013 2:22 PM
> > > > >
> > > > > On Wed, 2013-10-09 at 14:02 -0500, Yoder Stuart-B08248 wrote:
> > > > > > Have been thinking about this issue some more.  As Scott
> > > > > > mentioned,
> > 
> > thanks for bringing this up again.
> > 
> > > > > There's already a "bool suppress_bind_attrs" to prevent sysfs
> > > > > bind/unbind.  I suggested a similar flag to mean the oppsosite --
> > > > > bind
> > > > > *only* through sysfs.  Greg KH was skeptical and wanted to see a
> > > > > patch before any further discussion.
> > > >
> > > > Ah, think I understand now...yes that works as well, and would be
> > > > less intrustive.   So are you writing a patch? :)
> > >
> > > I've been meaning to since the previous round of discussion, but I've
> > > been busy.  Would someone else be able to test it in the context of
> > > using it for VFIO?
> > 
> > yes - see below.
> > 
> > > Otherwise, that looks about right, for the driver side (though
> > > driver_attach could error out earlier rather than testing it inside
> > > the loop).
> > 
> > I've made the changes you suggested and tested the resulting diff below on an
> > arndale board.  I successfully performed the following sequence of commands
> > after first changing the i2c@12C80000 node in the device tree to be exclusively
> > compatible with "vfio":

This is not the intended usage.  Leave the device tree alone, add a
wildcard option to platform_match() and use it in VFIO, and set
drv->sysfs_bind_only in VFIO.

> > diff --git a/drivers/base/bus.c b/drivers/base/bus.c index 73f6c29..da81442
> > 100644
> > --- a/drivers/base/bus.c
> > +++ b/drivers/base/bus.c
> > @@ -201,7 +201,8 @@ static ssize_t bind_store(struct device_driver *drv, const
> > char *buf,
> >  	int err = -ENODEV;
> > 
> >  	dev = bus_find_device_by_name(bus, NULL, buf);
> > -	if (dev && dev->driver == NULL && driver_match_device(drv, dev)) {
> > +	if (dev && dev->driver == NULL && (drv->sysfs_bind_only ||
> > +					   driver_match_device(drv, dev))) {
> 
> Should not we check 
>       if (dev && dev->driver == NULL &&
>           (device->explicit_bind_only && drv->explicit_bind_only) ||
>           driver_match_device(drv, dev)))

device->sysfs_bind_only would be a separate patch.

As for drv->sysfs_bind_only, that does not override
driver_match_device().  Wildcard matches are separate and are handled by
individual bus match functions.  This function does not need to be
changed at all for drv->sysfs_bind_only.

-Scott