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@xxxxxxxxxxxxxxxxxxxxxx> --- Documentation/ABI/testing/sysfs-bus-amba | 20 ++++++++++++++ drivers/amba/bus.c | 47 ++++++++++++++++++++++++++++++++ include/linux/amba/bus.h | 1 + 3 files changed, 68 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-bus-amba 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@xxxxxxxxxxxxxxxxxxxxxx> +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 3cf61a1..c7aa448 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 +63,47 @@ 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) \ @@ -80,6 +126,7 @@ 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 { -- 2.1.1 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
