driver core: platform: add device binding path 'driver_override'

Needed by platform device drivers, such as the upcoming
vfio-platform driver, 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", which is an interface enhancement
for more deterministic PCI device binding, e.g., when in the
presence of hotplug.

Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Stuart Yoder <stuart.yoder@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform
new file mode 100644 (file)
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@freescale.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-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 c48c4acb9b87ae78be1cb2a6dafda2bf23592b89..148f66a1d49a996543fc6fbf6ebc83b42869eb65 100644 (file)
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -23,6 +23,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/idr.h>
 #include <linux/acpi.h>
+#include <linux/limits.h>
 
 #include "base.h"
 #include "power/power.h"
@@ -191,6 +192,7 @@ static void platform_device_release(struct device *dev)
        kfree(pa->pdev.dev.platform_data);
        kfree(pa->pdev.mfd_cell);
        kfree(pa->pdev.resource);
+       kfree(pa->pdev.driver_override);
        kfree(pa);
 }
 
@@ -698,8 +700,49 @@ 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);
@@ -755,6 +798,10 @@ 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 16f6654082ddf82874a8531e51641d3bd62c1917..153d303af7ebc888a7f2fac4b75e3021162dd459 100644 (file)
--- 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;