Re: [RFC PATCH] PCI: Introduce new device binding path using pci_dev.driver_override

From: Guenter Roeck
Date: Fri Apr 04 2014 - 22:08:33 EST

On 04/04/2014 06:35 PM, Kim Phillips wrote:
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.


Signed-off-by: Kim Phillips <kim.phillips@xxxxxxxxxxxxx>
if this looks ok, should it be included in the next version of the
vfio-platform submission series, like last time ([1] above)?

Documentation/ABI/testing/sysfs-bus-platform | 17 ++++++++++
drivers/base/platform.c | 46 ++++++++++++++++++++++++++++
include/linux/platform_device.h | 1 +
3 files changed, 64 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..6b14a6a
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-platform
@@ -0,0 +1,17 @@
+What: /sys/bus/platform/devices/.../driver_override
+Date: April 2014
+Contact: Kim Phillips <kim.phillips@xxxxxxxxxxxxx>
+ 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 may be cleared by
+ writing an empty string (ex. echo > driver_override), returning
+ 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 name. If no driver with a matching name
+ is currently loaded in the kernel, no match will be found.
+ This also allows devices to opt-out of driver binding using
+ a driver_override name such as "none".
diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index e714709..ded1db1 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;
+ if (count > PATH_MAX)
+ return -EINVAL;
+ driver_override = kstrndup(buf, count, GFP_KERNEL);
+ if (!driver_override)
+ return -ENOMEM;
+ while (strlen(driver_override) &&
+ driver_override[strlen(driver_override) - 1] == '\n')
+ driver_override[strlen(driver_override) - 1] = '\0';

Seems to me that something like

cp = strchr(driver_override, '\n');
if (cp)
*cp = '\0';

would be much simpler.


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