Re: [PATCHv7 07/26] driver core: amba: add device binding path 'driver_override'

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 2014-09-23 at 16:46 +0200, Antonios Motakis wrote:
> As already demonstrated with PCI [1] and the platform bus [2], a
> driver_override property in sysfs can be used to bypass the id matching
> of a device to a AMBA driver. This can be used by VFIO to bind to any AMBA
> device requested by the user.
> 
> [1] http://lists-archives.com/linux-kernel/28030441-pci-introduce-new-device-binding-path-using-pci_dev-driver_override.html
> [2] https://www.redhat.com/archives/libvir-list/2014-April/msg00382.html
> 
> Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
> ---
>  drivers/amba/bus.c       | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/amba/bus.h |  1 +
>  2 files changed, 45 insertions(+)

Why are 7 & 8 being dragged into this series?  Combine them into a
single patch and post it separately.

> 
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index 3cf61a1..473177c 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -17,6 +17,7 @@
>  #include <linux/pm_runtime.h>
>  #include <linux/amba/bus.h>
>  #include <linux/sizes.h>
> +#include <linux/limits.h>
>  
>  #include <asm/irq.h>
>  
> @@ -42,6 +43,10 @@ static int amba_match(struct device *dev, struct device_driver *drv)
>  	struct amba_device *pcdev = to_amba_device(dev);
>  	struct amba_driver *pcdrv = to_amba_driver(drv);
>  
> +	/* When driver_override is set, only bind to the matching driver */
> +	if (pcdev->driver_override)
> +		return !strcmp(pcdev->driver_override, drv->name);
> +
>  	return amba_lookup(pcdrv->id_table, pcdev) != NULL;
>  }
>  
> @@ -58,6 +63,44 @@ static int amba_uevent(struct device *dev, struct kobj_uevent_env *env)
>  	return retval;
>  }
>  
> +static ssize_t driver_override_show(struct device *_dev,
> +				    struct device_attribute *attr, char *buf)
> +{
> +	struct amba_device *dev = to_amba_device(_dev);
> +
> +	return sprintf(buf, "%s\n", dev->driver_override);
> +}
> +
> +static ssize_t driver_override_store(struct device *_dev,
> +				     struct device_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	struct amba_device *dev = to_amba_device(_dev);
> +	char *driver_override, *old = dev->driver_override, *cp;
> +
> +	if (count > PATH_MAX)
> +		return -EINVAL;
> +
> +	driver_override = kstrndup(buf, count, GFP_KERNEL);
> +	if (!driver_override)
> +		return -ENOMEM;
> +
> +	cp = strchr(driver_override, '\n');
> +	if (cp)
> +		*cp = '\0';
> +
> +	if (strlen(driver_override)) {
> +		dev->driver_override = driver_override;
> +	} else {
> +	       kfree(driver_override);
> +	       dev->driver_override = NULL;
> +	}
> +
> +	kfree(old);
> +
> +	return count;
> +}
> +
>  #define amba_attr_func(name,fmt,arg...)					\
>  static ssize_t name##_show(struct device *_dev,				\
>  			   struct device_attribute *attr, char *buf)	\
> @@ -80,6 +123,7 @@ amba_attr_func(resource, "\t%016llx\t%016llx\t%016lx\n",
>  static struct device_attribute amba_dev_attrs[] = {
>  	__ATTR_RO(id),
>  	__ATTR_RO(resource),
> +	__ATTR_RW(driver_override),
>  	__ATTR_NULL,
>  };
>  
> diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
> index fdd7e1b..7c011e7 100644
> --- a/include/linux/amba/bus.h
> +++ b/include/linux/amba/bus.h
> @@ -32,6 +32,7 @@ struct amba_device {
>  	struct clk		*pclk;
>  	unsigned int		periphid;
>  	unsigned int		irq[AMBA_NR_IRQS];
> +	char			*driver_override;
>  };
>  
>  struct amba_driver {