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: Antonios Motakis <a.motakis@virtualopensystems.com>
Reviewed-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/Documentation/ABI/testing/sysfs-bus-amba b/Documentation/ABI/testing/sysfs-bus-amba
new file mode 100644 (file)
index 0000000..e7b5467
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-amba
@@ -0,0 +1,20 @@
+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.

diff --cc drivers/amba/bus.c
Simple merge

diff --cc include/linux/amba/bus.h
Simple merge