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>

1 files changed, 47 insertions, 0 deletions

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index c48c4acb9b87..148f66a1d49a 100644
--- 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;