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Commit 3cf38571 authored by Antonios Motakis's avatar Antonios Motakis Committed by Russell King
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ARM: 8256/1: driver coamba: add device binding path 'driver_override' 

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: default avatarAntonios Motakis <a.motakis@virtualopensystems.com>
Reviewed-by: default avatarKim Phillips <kim.phillips@freescale.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 8684014d

Documentation/ABI/testing/sysfs-bus-amba

0 → 100644
+20 −0
Original line number Diff line number Diff line 
What:		/sys/bus/amba/devices/.../driver_override

Date:		September 2014

Contact:	Antonios Motakis <a.motakis@virtualopensystems.com>

Description:

		This file allows the driver for a device to be specified which

		will override standard OF, ACPI, ID table, and name matching.

		When specified, only a driver with a name matching the value

		written to driver_override will have an opportunity to bind to

		the device. The override is specified by writing a string to the

		driver_override file (echo vfio-amba > driver_override)	and may

		be cleared with an empty string (echo > driver_override).

		This returns the device to standard matching rules binding.

		Writing to driver_override does not automatically unbind the

		device from its current driver or make any attempt to

		automatically load the specified driver. If no driver with a

		matching name is currently loaded in the kernel, the device will

		not bind to any driver. This also allows devices to opt-out of

		driver binding using a driver_override name such as "none".

		Only a single driver may be specified in the override, there is

		no support for parsing delimiters.

drivers/amba/bus.c

+47 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
#include <linux/pm_domain.h>

#include <linux/amba/bus.h>

#include <linux/sizes.h>

#include <linux/limits.h>



#include <asm/irq.h>
@@ -43,6 +44,10 @@ 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;

}
@@ -59,6 +64,47 @@ 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);



	if (!dev->driver_override)

		return 0;



	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)	\
@@ -81,6 +127,7 @@ 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,

};

include/linux/amba/bus.h

+1 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ struct amba_device { 
	struct clk		*pclk;

	unsigned int		periphid;

	unsigned int		irq[AMBA_NR_IRQS];

	char			*driver_override;

};



struct amba_driver {