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
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 --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index 52ddd9f..f009936 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -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 @@
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 @@
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 @@
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 0ab5f8e..50fc668 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -33,6 +33,7 @@
struct clk *pclk;
unsigned int periphid;
unsigned int irq[AMBA_NR_IRQS];
+ char *driver_override;
};
struct amba_driver {