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

[Yoder Stuart-B08248]

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Wednesday, October 09, 2013 2:22 PM
> To: Yoder Stuart-B08248
> Cc: Wood Scott-B07421; Kim Phillips; Christoffer Dall; Alex Williamson;
> linux-kernel@xxxxxxxxxxxxxxx; a.motakis@xxxxxxxxxxxxxxxxxxxxxx;
> agraf@xxxxxxx; Sethi Varun-B16395; Bhushan Bharat-R65777;
> peter.maydell@xxxxxxxxxx; santosh.shukla@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx;
> gregkh@xxxxxxxxxxxxxxxxxxx
> Subject: Re: RFC: (re-)binding the VFIO platform driver to a platform
> device
> 
> On Wed, 2013-10-09 at 14:02 -0500, Yoder Stuart-B08248 wrote:
> > Have been thinking about this issue some more.  As Scott mentioned,
> > 'wildcard' matching for a driver can be fairly done in the platform
> > bus driver.  We could add a new flag to the platform driver struct:
> >
> > diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> > index 4f8bef3..4d6cf14 100644
> > --- a/drivers/base/platform.c
> > +++ b/drivers/base/platform.c
> > @@ -727,6 +727,10 @@ 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)
> > +               return 1;
> > +
> >         /* Attempt an OF style match first */
> >         if (of_driver_match_device(dev, drv))
> >                 return 1;
> >
> > However, the more problematic issue is that a bus driver has no way to
> > differentiate from an explicit bind request via sysfs and a bind that
> > happened through bus probing.
> 
> Again, I think the wildcard match should be orthogonal to "don't bind by
> default" as far as the mechanism goes.
> 
> 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? :)

It would be something like this, right?

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 35fa368..c9a61ea 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -389,7 +389,7 @@ static int __device_attach(struct device_driver *drv, void *data)
 {
        struct device *dev = data;

-       if (!driver_match_device(drv, dev))
+       if (!drv->explicit_bind_only && !driver_match_device(drv, dev))
                return 0;

        return driver_probe_device(drv, dev);
@@ -450,7 +450,7 @@ static int __driver_attach(struct device *dev, void *data)
         * is an error.
         */

-       if (!driver_match_device(drv, dev))
+       if (!drv->explicit_bind_only && !driver_match_device(drv, dev))
                return 0;

        if (dev->parent)        /* Needed for USB */
diff --git a/include/linux/device.h b/include/linux/device.h
index 2a9d6ed..f2be980 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -236,6 +236,7 @@ struct device_driver {
        const char              *mod_name;      /* used for built-in modules */

        bool suppress_bind_attrs;       /* disables bind/unbind via sysfs */
+       bool explicit_bind_only;        /* enables bind/unbind via sysfs only */

        const struct of_device_id       *of_match_table;
        const struct acpi_device_id     *acpi_match_table;


Stuart


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