Re: [REPOST][PATCH 2/2] driver core: platform: allow platform drivers to bind to any device

[Scott Wood <scottwood@freescale.com>]

On Wed, 2013-12-18 at 17:03 -0800, Greg Kroah-Hartman wrote:
> On Tue, Dec 03, 2013 at 12:34:54PM +0000, Kim Phillips wrote:
> > Platform drivers such as the vfio-platform "meta-" driver [1]
> > should be allowed to specify that they can bind to any device,
> > much like PCI drivers can with PCI_ANY_ID.
> > 
> > Currently, binding platform drivers to devices depends on:
> > 
> > - a string match in the device node's compatible entry (OF)
> > - a string match in the ACPI id list (ACPI)
> > - a string match in the id_table (platform data)
> > - a string match on the driver name (fall-back)
> > 
> > none of which allow for the notion of "match any."
> > 
> > This patch adds the notion by adding a "match any device" boolean to
> > struct platform_driver, for drivers to be able to set and thus not cause
> > platform_match() to fail when a bind is requested.
> > 
> > [1] http://www.spinics.net/lists/kvm/msg96701.html
> > 
> > Signed-off-by: Kim Phillips <kim.phillips@linaro.org>
> > ---
> > rebased onto 3.13-rc2, and reposted from first submission which
> > received no comments:
> > 
> > https://lkml.org/lkml/2013/10/11/48
> > 
> >  drivers/base/platform.c         | 4 ++++
> >  include/linux/platform_device.h | 1 +
> >  2 files changed, 5 insertions(+)
> > 
> > diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> > index 3a94b79..78a5b62 100644
> > --- a/drivers/base/platform.c
> > +++ b/drivers/base/platform.c
> > @@ -736,6 +736,10 @@ static int platform_match(struct device *dev, struct device_driver *drv)
> >  	struct platform_device *pdev = to_platform_device(dev);
> >  	struct platform_driver *pdrv = to_platform_driver(drv);
> >  
> > +	/* the driver matches any device */
> > +	if (pdrv->match_any_dev)
> > +		return 1;
> 
> This breaks userspace in that it will never know to load the module that
> can "bind to anything".
> 
> You need a way to encode this in the platform device id that can be a
> wildcard type of thing, so that userspace can know about this.

How is userspace broken?  vfio platform is a new thing; there's nothing
existing to break.  I don't see how automatic module loading makes sense
for it.  Whether the module needs to be loaded depends on the user's
intentions, not based on what hardware you have.

-Scott