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

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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>
This commit is contained in:
Kim Phillips 2014-06-02 19:42:58 -05:00 committed by Greg Kroah-Hartman
parent 1cec24c59b
commit 3d713e0e38
3 changed files with 68 additions and 0 deletions
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20
Documentation/ABI/testing/sysfs-bus-platform Normal file
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@ -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.

47
drivers/base/platform.c
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@ -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;

1
include/linux/platform_device.h
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@ -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;