Needed by platform device drivers, such as the vfio-platform driver [1], in order to bypass the existing OF, ACPI, id_table and name string matches, and successfully be able to be bound to any device, like so: echo vfio-platform > /sys/bus/platform/devices/fff51000.ethernet/driver_override echo fff51000.ethernet > /sys/bus/platform/devices/fff51000.ethernet/driver/unbind echo fff51000.ethernet > /sys/bus/platform/drivers_probe This mimics "PCI: Introduce new device binding path using pci_dev.driver_override" [2], which is an interface enhancement for more deterministic PCI device binding, e.g., when in the presence of hotplug. [1] http://lkml.iu.edu/hypermail/linux/kernel/1402.1/00177.html [2] http://lists-archives.com/linux-kernel/28030441-pci-introduce-new-device-binding-path-using-pci_dev-driver_override.html Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx> Signed-off-by: Kim Phillips <kim.phillips@xxxxxxxxxxxxx> --- changes since RFC: - fixed message Subject to properly reflect a new platform device patch (instead of leaving it as a reply to the PCI version) - addressed Guenter Roeck's comment - updated [2] with link to later (Apr.4th) revision of the PCI patch - updated documentation to address Christoffer Dall's comments to previous version of [2] - added a Suggested-by, and re-posted as a reply to the PCI patch, should they be applied together Documentation/ABI/testing/sysfs-bus-platform | 20 ++++++++++++ drivers/base/platform.c | 46 ++++++++++++++++++++++++++++ include/linux/platform_device.h | 1 + 3 files changed, 67 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-bus-platform diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform new file mode 100644 index 0000000..5172a61 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-bus-platform @@ -0,0 +1,20 @@ +What: /sys/bus/platform/devices/.../driver_override +Date: April 2014 +Contact: Kim Phillips <kim.phillips@xxxxxxxxxxxxx> +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-platform > \ + 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/base/platform.c b/drivers/base/platform.c index e714709..a0909cb 100644 --- a/drivers/base/platform.c +++ b/drivers/base/platform.c @@ -22,6 +22,7 @@ #include <linux/pm_runtime.h> #include <linux/idr.h> #include <linux/acpi.h> +#include <linux/limits.h> #include "base.h" #include "power/power.h" @@ -690,8 +691,49 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *a, } static DEVICE_ATTR_RO(modalias); +static ssize_t driver_override_store(struct device *dev, + struct device_attribute *attr, + const char *buf, size_t count) +{ + struct platform_device *pdev = to_platform_device(dev); + char *driver_override, *old = pdev->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)) { + pdev->driver_override = driver_override; + } else { + kfree(driver_override); + pdev->driver_override = NULL; + } + + kfree(old); + + return count; +} + +static ssize_t driver_override_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + struct platform_device *pdev = to_platform_device(dev); + + return sprintf(buf, "%s\n", pdev->driver_override); +} +static DEVICE_ATTR_RW(driver_override); + + static struct attribute *platform_dev_attrs[] = { &dev_attr_modalias.attr, + &dev_attr_driver_override.attr, NULL, }; ATTRIBUTE_GROUPS(platform_dev); @@ -747,6 +789,10 @@ static int platform_match(struct device *dev, struct device_driver *drv) struct platform_device *pdev = to_platform_device(dev); struct platform_driver *pdrv = to_platform_driver(drv); + /* When driver_override is set, only bind to the matching driver */ + if (pdev->driver_override) + return !strcmp(pdev->driver_override, drv->name); + /* Attempt an OF style match first */ if (of_driver_match_device(dev, drv)) return 1; diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h index 16f6654..153d303 100644 --- a/include/linux/platform_device.h +++ b/include/linux/platform_device.h @@ -28,6 +28,7 @@ struct platform_device { struct resource *resource; const struct platform_device_id *id_entry; + char *driver_override; /* Driver name to force a match */ /* MFD cell pointer */ struct mfd_cell *mfd_cell; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
