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

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Date:	Wed, 9 Oct 2013 14:21:47 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Yoder Stuart-B08248 <B08248@...escale.com>
CC:	Wood Scott-B07421 <B07421@...escale.com>,
	Kim Phillips <kim.phillips@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"a.motakis@...tualopensystems.com" <a.motakis@...tualopensystems.com>,
	"agraf@...e.de" <agraf@...e.de>,
	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>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
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.

> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 2cbc677..7a15ef3 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -114,9 +114,9 @@ extern void driver_detach(struct device_driver *drv);
>  extern int driver_probe_device(struct device_driver *drv, struct device *dev);
>  extern void driver_deferred_probe_del(struct device *dev);
>  static inline int driver_match_device(struct device_driver *drv,
> -                                     struct device *dev)
> +                                     struct device *dev, int explicit_bind)
>  {
> -       return drv->bus->match ? drv->bus->match(dev, drv) : 1;
> +       return drv->bus->match ? drv->bus->match(dev, drv, explicit_bind) : 1;
>  }
> 
> Of, course the above change would need to be propagated to the different
> bus drivers that implement the 'match' function.

...which would not be a problem with my approach, because you could
handle it in the callers of driver_match_device().

-Scott



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