[PATCH v2 02/13] vfio/mdev: Allow the mdev_parent_ops to specify the device driver to bind

[Jason Gunthorpe <jgg@nvidia.com>]

This allows a mdev driver to opt out of using vfio_mdev.c, instead the
driver will provide a 'struct mdev_driver' and register directly with the
driver core.

Much of mdev_parent_ops becomes unused in this mode:
- create()/remove() are done via the mdev_driver probe()/remove()
- mdev_attr_groups becomes mdev_driver driver.dev_groups
- Wrapper function callbacks are replaced with the same ones from
  struct vfio_device_ops

Following patches convert all the drivers.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 drivers/vfio/mdev/mdev_core.c   | 64 ++++++++++++++++++++++++++++-----
 drivers/vfio/mdev/mdev_driver.c | 17 ++++++++-
 include/linux/mdev.h            |  3 ++
 3 files changed, 75 insertions(+), 9 deletions(-)

diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
index ff8c1a84516698..51b8a9fcf866ad 100644
--- a/drivers/vfio/mdev/mdev_core.c
+++ b/drivers/vfio/mdev/mdev_core.c
@@ -94,9 +94,11 @@ static void mdev_device_remove_common(struct mdev_device *mdev)
 	mdev_remove_sysfs_files(mdev);
 	device_del(&mdev->dev);
 	lockdep_assert_held(&parent->unreg_sem);
-	ret = parent->ops->remove(mdev);
-	if (ret)
-		dev_err(&mdev->dev, "Remove failed: err=%d\n", ret);
+	if (parent->ops->remove) {
+		ret = parent->ops->remove(mdev);
+		if (ret)
+			dev_err(&mdev->dev, "Remove failed: err=%d\n", ret);
+	}
 
 	/* Balances with device_initialize() */
 	put_device(&mdev->dev);
@@ -127,7 +129,9 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops)
 	char *envp[] = { env_string, NULL };
 
 	/* check for mandatory ops */
-	if (!ops || !ops->create || !ops->remove || !ops->supported_type_groups)
+	if (!ops || !ops->supported_type_groups)
+		return -EINVAL;
+	if (!ops->device_driver && (!ops->create || !ops->remove))
 		return -EINVAL;
 
 	dev = get_device(dev);
@@ -251,6 +255,43 @@ static void mdev_device_release(struct device *dev)
 	kfree(mdev);
 }
 
+/*
+ * mdev drivers can refuse to bind during probe(), in this case we want to fail
+ * the creation of the mdev all the way back to sysfs. This is a weird model
+ * that doesn't fit in the driver core well, nor does it seem to appear any
+ * place else in the kernel, so use a simple hack.
+ */
+static int mdev_bind_driver(struct mdev_device *mdev)
+{
+	struct mdev_driver *drv = mdev->type->parent->ops->device_driver;
+	int ret;
+
+	if (!drv)
+		drv = &vfio_mdev_driver;
+
+	while (1) {
+		device_lock(&mdev->dev);
+		if (mdev->dev.driver == &drv->driver) {
+			ret = 0;
+			goto out_unlock;
+		}
+		if (mdev->probe_err) {
+			ret = mdev->probe_err;
+			goto out_unlock;
+		}
+		device_unlock(&mdev->dev);
+		ret = device_attach(&mdev->dev);
+		if (ret)
+			return ret;
+		mdev->probe_err = -EINVAL;
+	}
+	return 0;
+
+out_unlock:
+	device_unlock(&mdev->dev);
+	return ret;
+}
+
 int mdev_device_create(struct mdev_type *type, const guid_t *uuid)
 {
 	int ret;
@@ -296,14 +337,20 @@ int mdev_device_create(struct mdev_type *type, const guid_t *uuid)
 		goto out_put_device;
 	}
 
-	ret = parent->ops->create(mdev);
-	if (ret)
-		goto out_unlock;
+	if (parent->ops->create) {
+		ret = parent->ops->create(mdev);
+		if (ret)
+			goto out_unlock;
+	}
 
 	ret = device_add(&mdev->dev);
 	if (ret)
 		goto out_remove;
 
+	ret = mdev_bind_driver(mdev);
+	if (ret)
+		goto out_del;
+
 	ret = mdev_create_sysfs_files(mdev);
 	if (ret)
 		goto out_del;
@@ -317,7 +364,8 @@ int mdev_device_create(struct mdev_type *type, const guid_t *uuid)
 out_del:
 	device_del(&mdev->dev);
 out_remove:
-	parent->ops->remove(mdev);
+	if (parent->ops->remove)
+		parent->ops->remove(mdev);
 out_unlock:
 	up_read(&parent->unreg_sem);
 out_put_device:
diff --git a/drivers/vfio/mdev/mdev_driver.c b/drivers/vfio/mdev/mdev_driver.c
index 041699571b7e55..6e96c023d7823d 100644
--- a/drivers/vfio/mdev/mdev_driver.c
+++ b/drivers/vfio/mdev/mdev_driver.c
@@ -49,7 +49,7 @@ static int mdev_probe(struct device *dev)
 		return ret;
 
 	if (drv->probe) {
-		ret = drv->probe(mdev);
+		ret = mdev->probe_err = drv->probe(mdev);
 		if (ret)
 			mdev_detach_iommu(mdev);
 	}
@@ -71,10 +71,25 @@ static int mdev_remove(struct device *dev)
 	return 0;
 }
 
+static int mdev_match(struct device *dev, struct device_driver *drv)
+{
+	struct mdev_device *mdev = to_mdev_device(dev);
+	struct mdev_driver *target = mdev->type->parent->ops->device_driver;
+
+	/*
+	 * The ops specify the device driver to connect, fall back to the old
+	 * shim driver if the driver hasn't been converted.
+	 */
+	if (!target)
+		target = &vfio_mdev_driver;
+	return drv == &target->driver;
+}
+
 struct bus_type mdev_bus_type = {
 	.name		= "mdev",
 	.probe		= mdev_probe,
 	.remove		= mdev_remove,
+	.match		= mdev_match,
 };
 EXPORT_SYMBOL_GPL(mdev_bus_type);
 
diff --git a/include/linux/mdev.h b/include/linux/mdev.h
index 1fb34ea394ad46..49cc4f65120d57 100644
--- a/include/linux/mdev.h
+++ b/include/linux/mdev.h
@@ -19,6 +19,7 @@ struct mdev_device {
 	struct list_head next;
 	struct mdev_type *type;
 	struct device *iommu_device;
+	int probe_err;
 	bool active;
 };
 
@@ -55,6 +56,7 @@ struct device *mtype_get_parent_dev(struct mdev_type *mtype);
  * register the device to mdev module.
  *
  * @owner:		The module owner.
+ * @device_driver:	Which device driver to probe() on newly created devices
  * @dev_attr_groups:	Attributes of the parent device.
  * @mdev_attr_groups:	Attributes of the mediated device.
  * @supported_type_groups: Attributes to define supported types. It is mandatory
@@ -103,6 +105,7 @@ struct device *mtype_get_parent_dev(struct mdev_type *mtype);
  **/
 struct mdev_parent_ops {
 	struct module   *owner;
+	struct mdev_driver *device_driver;
 	const struct attribute_group **dev_attr_groups;
 	const struct attribute_group **mdev_attr_groups;
 	struct attribute_group **supported_type_groups;
-- 
2.31.1