[PATCH 4/5] driver core: inhibit automatic driver binding on reserved devices

[Zev Weiss]

Devices whose fwnodes are marked as reserved are instantiated, but
will not have a driver bound to them unless userspace explicitly
requests it by writing to a 'bind' sysfs file.  This is to enable
devices that may require special (userspace-mediated) preparation
before a driver can safely probe them.

Signed-off-by: Zev Weiss <zev at bewilderbeest.net>
---
 drivers/base/bus.c            |  2 +-
 drivers/base/dd.c             | 13 ++++++++-----
 drivers/dma/idxd/compat.c     |  3 +--
 drivers/vfio/mdev/mdev_core.c |  2 +-
 include/linux/device.h        | 14 +++++++++++++-
 5 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index bdc98c5713d5..8a30f9a02de0 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -211,7 +211,7 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf,
 
 	dev = bus_find_device_by_name(bus, NULL, buf);
 	if (dev && driver_match_device(drv, dev)) {
-		err = device_driver_attach(drv, dev);
+		err = device_driver_attach(drv, dev, DRV_BIND_EXPLICIT);
 		if (!err) {
 			/* success */
 			err = count;
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 68ea1f949daa..ee64740a63d9 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -22,6 +22,7 @@
 #include <linux/dma-map-ops.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/property.h>
 #include <linux/kthread.h>
 #include <linux/wait.h>
 #include <linux/async.h>
@@ -727,13 +728,14 @@ void wait_for_device_probe(void)
 }
 EXPORT_SYMBOL_GPL(wait_for_device_probe);
 
-static int __driver_probe_device(struct device_driver *drv, struct device *dev)
+static int __driver_probe_device(struct device_driver *drv, struct device *dev, u32 flags)
 {
 	int ret = 0;
 
 	if (dev->p->dead || !device_is_registered(dev))
 		return -ENODEV;
-	if (dev->driver)
+	if (dev->driver ||
+	    (fwnode_device_is_reserved(dev->fwnode) && !(flags & DRV_BIND_EXPLICIT)))
 		return -EBUSY;
 
 	dev->can_match = true;
@@ -778,7 +780,7 @@ static int driver_probe_device(struct device_driver *drv, struct device *dev)
 	int ret;
 
 	atomic_inc(&probe_count);
-	ret = __driver_probe_device(drv, dev);
+	ret = __driver_probe_device(drv, dev, DRV_BIND_DEFAULT);
 	if (ret == -EPROBE_DEFER || ret == EPROBE_DEFER) {
 		driver_deferred_probe_add(dev);
 
@@ -1052,16 +1054,17 @@ static void __device_driver_unlock(struct device *dev, struct device *parent)
  * device_driver_attach - attach a specific driver to a specific device
  * @drv: Driver to attach
  * @dev: Device to attach it to
+ * @flags: Bitmask of DRV_BIND_* flags
  *
  * Manually attach driver to a device. Will acquire both @dev lock and
  * @dev->parent lock if needed. Returns 0 on success, -ERR on failure.
  */
-int device_driver_attach(struct device_driver *drv, struct device *dev)
+int device_driver_attach(struct device_driver *drv, struct device *dev, u32 flags)
 {
 	int ret;
 
 	__device_driver_lock(dev, dev->parent);
-	ret = __driver_probe_device(drv, dev);
+	ret = __driver_probe_device(drv, dev, flags);
 	__device_driver_unlock(dev, dev->parent);
 
 	/* also return probe errors as normal negative errnos */
diff --git a/drivers/dma/idxd/compat.c b/drivers/dma/idxd/compat.c
index 3df21615f888..51df38dea15a 100644
--- a/drivers/dma/idxd/compat.c
+++ b/drivers/dma/idxd/compat.c
@@ -7,7 +7,6 @@
 #include <linux/device/bus.h>
 #include "idxd.h"
 
-extern int device_driver_attach(struct device_driver *drv, struct device *dev);
 extern void device_driver_detach(struct device *dev);
 
 #define DRIVER_ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store)	\
@@ -56,7 +55,7 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf, size_t cou
 	if (!alt_drv)
 		return -ENODEV;
 
-	rc = device_driver_attach(alt_drv, dev);
+	rc = device_driver_attach(alt_drv, dev, DRV_BIND_EXPLICIT);
 	if (rc < 0)
 		return rc;
 
diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
index b314101237fe..f42c6ec543c8 100644
--- a/drivers/vfio/mdev/mdev_core.c
+++ b/drivers/vfio/mdev/mdev_core.c
@@ -309,7 +309,7 @@ int mdev_device_create(struct mdev_type *type, const guid_t *uuid)
 
 	if (!drv)
 		drv = &vfio_mdev_driver;
-	ret = device_driver_attach(&drv->driver, &mdev->dev);
+	ret = device_driver_attach(&drv->driver, &mdev->dev, DRV_BIND_DEFAULT);
 	if (ret)
 		goto out_del;
 
diff --git a/include/linux/device.h b/include/linux/device.h
index e270cb740b9e..1ada1093799b 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -876,12 +876,24 @@ static inline void *dev_get_platdata(const struct device *dev)
 	return dev->platform_data;
 }
 
+/*
+ * Driver-binding flags (for passing to device_driver_attach())
+ *
+ * DRV_BIND_DEFAULT: a default, automatic bind, e.g. as a result of a device
+ *                   being added for which we already have a driver, or vice
+ *                   versa.
+ * DRV_BIND_EXPLICIT: an explicit, userspace-requested driver bind, e.g. as a
+ *                    result of a write to /sys/bus/.../drivers/.../bind
+ */
+#define DRV_BIND_DEFAULT	0
+#define DRV_BIND_EXPLICIT	BIT(0)
+
 /*
  * Manual binding of a device to driver. See drivers/base/bus.c
  * for information on use.
  */
 int __must_check device_driver_attach(struct device_driver *drv,
-				      struct device *dev);
+				      struct device *dev, u32 flags);
 int __must_check device_bind_driver(struct device *dev);
 void device_release_driver(struct device *dev);
 int  __must_check device_attach(struct device *dev);
-- 
2.33.1