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Date:	Fri, 4 Apr 2014 20:35:12 -0500
From:	Kim Phillips <kim.phillips@...escale.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	Kim Phillips <kim.phillips@...aro.org>,
	<gregkh@...uxfoundation.org>, <stuart.yoder@...escale.com>,
	<kvm@...r.kernel.org>, <jan.kiszka@...mens.com>,
	<will.deacon@....com>, <linux-kernel@...r.kernel.org>,
	<mhocko@...e.cz>, <bhelgaas@...gle.com>,
	<Varun.Sethi@...escale.com>, <kvmarm@...ts.cs.columbia.edu>,
	<rafael.j.wysocki@...el.com>, <agraf@...e.de>,
	<linux-pci@...r.kernel.org>, <linux@...ck-us.net>,
	<konrad.wilk@...cle.com>, <d.kasatkin@...sung.com>,
	<tj@...nel.org>, <scottwood@...escale.com>,
	<a.motakis@...tualopensystems.com>, <tech@...tualopensystems.com>,
	<Bharat.Bhushan@...escale.com>, <toshi.kani@...com>,
	<a.rigo@...tualopensystems.com>,
	<iommu@...ts.linux-foundation.org>, <joe@...ches.com>,
	<christoffer.dall@...aro.org>
Subject: Re: [RFC PATCH] PCI: Introduce new device binding path using
 pci_dev.driver_override

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://thread.gmane.org/gmane.linux.kernel.iommu/4605

Signed-off-by: Kim Phillips <kim.phillips@...escale.com>
---
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@...escale.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 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';
+
+	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


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