Media Device Allocator API to allows multiple drivers share a media device.
Using this API, drivers can allocate a media device with the shared struct
device as the key. Once the media device is allocated by a driver, other
drivers can get a reference to it. The media device is released when all
the references are released.
Signed-off-by: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
Reviewed-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
Changes since v3:
- Fixed undefined reference to `__media_device_usb_init compile error when
CONFIG_USB is disabled.
- Fixed kernel paging error when accessing /dev/mediaX after rmmod of the
module that owns the media_device. The fix bumps the reference count for
the owner when second driver comes along to share the media_device. If
au0828 owns the media_device, then snd_usb_audio will bump the refcount
for au0828, so it won't get deleted and vice versa.
drivers/media/Makefile | 3 +-
drivers/media/media-dev-allocator.c | 146 ++++++++++++++++++++++++++++++++++++
include/media/media-dev-allocator.h | 87 +++++++++++++++++++++
3 files changed, 235 insertions(+), 1 deletion(-)
create mode 100644 drivers/media/media-dev-allocator.c
create mode 100644 include/media/media-dev-allocator.h
diff --git a/drivers/media/Makefile b/drivers/media/Makefile
index 0deaa93..7c0701d 100644
--- a/drivers/media/Makefile
+++ b/drivers/media/Makefile
@@ -6,7 +6,8 @@ ifeq ($(CONFIG_MEDIA_CEC_EDID),y)
obj-$(CONFIG_MEDIA_SUPPORT) += cec-edid.o
endif
-media-objs := media-device.o media-devnode.o media-entity.o
+media-objs := media-device.o media-devnode.o media-entity.o \
+ media-dev-allocator.o
#
# I2C drivers should come before other drivers, otherwise they'll fail
diff --git a/drivers/media/media-dev-allocator.c b/drivers/media/media-dev-allocator.c
new file mode 100644
index 0000000..014a317
--- /dev/null
+++ b/drivers/media/media-dev-allocator.c
@@ -0,0 +1,146 @@
+/*
+ * media-dev-allocator.c - Media Controller Device Allocator API
+ *
+ * Copyright (c) 2016 Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
+ * Copyright (c) 2016 Samsung Electronics Co., Ltd.
+ *
+ * This file is released under the GPLv2.
+ * Credits: Suggested by Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
+ */
+
+/*
+ * This file adds a global refcounted Media Controller Device Instance API.
+ * A system wide global media device list is managed and each media device
+ * includes a kref count. The last put on the media device releases the media
+ * device instance.
+ *
+ */
+
+#include <linux/slab.h>
+#include <linux/kref.h>
+#include <linux/usb.h>
+#include <linux/module.h>
+#include <media/media-device.h>
+
+static LIST_HEAD(media_device_list);
+static DEFINE_MUTEX(media_device_lock);
+
+struct media_device_instance {
+ struct media_device mdev;
+ struct module *owner;
+ struct list_head list;
+ struct device *dev;
+ struct kref refcount;
+};
+
+static inline struct media_device_instance *
+to_media_device_instance(struct media_device *mdev)
+{
+ return container_of(mdev, struct media_device_instance, mdev);
+}
+
+static void media_device_instance_release(struct kref *kref)
+{
+ struct media_device_instance *mdi =
+ container_of(kref, struct media_device_instance, refcount);
+
+ dev_dbg(mdi->mdev.dev, "%s: mdev=%p\n", __func__, &mdi->mdev);
+
+ mutex_lock(&media_device_lock);
+
+ media_device_unregister(&mdi->mdev);
+ media_device_cleanup(&mdi->mdev);
+
+ list_del(&mdi->list);
+ mutex_unlock(&media_device_lock);
+
+ kfree(mdi);
+}
+
+/* Callers should hold media_device_lock when calling this function */
+static struct media_device *__media_device_get(struct device *dev,
+ char *module_name)
+{
+ struct media_device_instance *mdi;
+
+ list_for_each_entry(mdi, &media_device_list, list) {
+ if (mdi->dev == dev) {
+ kref_get(&mdi->refcount);
+ /* get module reference for the media_device owner */
+ if (find_module(module_name) != mdi->owner &&
+ !try_module_get(mdi->owner))
+ dev_err(dev, "%s: try_module_get() error\n",
+ __func__);
+ dev_dbg(dev, "%s: get mdev=%p module_name %s\n",
+ __func__, &mdi->mdev, module_name);
+ return &mdi->mdev;
+ }
+ }
+
+ mdi = kzalloc(sizeof(*mdi), GFP_KERNEL);
+ if (!mdi)
+ return NULL;
+
+ mdi->dev = dev;
+ mdi->owner = find_module(module_name);
+ kref_init(&mdi->refcount);
+ list_add_tail(&mdi->list, &media_device_list);
+
+ dev_dbg(dev, "%s: alloc mdev=%p module_name %s\n", __func__,
+ &mdi->mdev, module_name);
+ return &mdi->mdev;
+}
+
+#if IS_ENABLED(CONFIG_USB)
+struct media_device *media_device_usb_allocate(struct usb_device *udev,
+ char *module_name)
+{
+ struct media_device *mdev;
+
+ if (!module_name) {
+ dev_err(&udev->dev, "%s Module Name is null\n", __func__);
+ return ERR_PTR(-EINVAL);
+ }
+
+ mutex_lock(&media_device_lock);
+ mdev = __media_device_get(&udev->dev, module_name);
+ if (!mdev) {
+ mutex_unlock(&media_device_lock);
+ return ERR_PTR(-ENOMEM);
+ }
+
+ /* check if media device is already initialized */
+ if (!mdev->dev)
+ __media_device_usb_init(mdev, udev, udev->product,
+ module_name);
+ mutex_unlock(&media_device_lock);
+
+ dev_dbg(&udev->dev, "%s\n", __func__);
+ return mdev;
+}
+EXPORT_SYMBOL_GPL(media_device_usb_allocate);
+#endif
+
+void media_device_delete(struct media_device *mdev, char *module_name)
+{
+ struct media_device_instance *mdi = to_media_device_instance(mdev);
+
+ if (!module_name) {
+ dev_err(mdi->mdev.dev, "%s Module Name is null\n", __func__);
+ return;
+ }
+
+ dev_dbg(mdi->mdev.dev, "%s: mdev=%p module_name %s\n",
+ __func__, &mdi->mdev, module_name);
+
+ mutex_lock(&media_device_lock);
+ /* put module reference if media_device owner is not THIS_MODULE */
+ if (mdi->owner != find_module(module_name)) {
+ module_put(mdi->owner);
+ dev_dbg(mdi->mdev.dev,
+ "%s decremented owner module reference\n", __func__);
+ }
+ mutex_unlock(&media_device_lock);
+ kref_put(&mdi->refcount, media_device_instance_release);
+}
+EXPORT_SYMBOL_GPL(media_device_delete);
diff --git a/include/media/media-dev-allocator.h b/include/media/media-dev-allocator.h
new file mode 100644
index 0000000..45c437d
--- /dev/null
+++ b/include/media/media-dev-allocator.h
@@ -0,0 +1,87 @@
+/*
+ * media-dev-allocator.h - Media Controller Device Allocator API
+ *
+ * Copyright (c) 2016 Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
+ * Copyright (c) 2016 Samsung Electronics Co., Ltd.
+ *
+ * This file is released under the GPLv2.
+ * Credits: Suggested by Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
+ */
+
+/*
+ * This file adds a global ref-counted Media Controller Device Instance API.
+ * A system wide global media device list is managed and each media device
+ * includes a kref count. The last put on the media device releases the media
+ * device instance.
+ */
+
+#ifndef _MEDIA_DEV_ALLOCTOR_H
+#define _MEDIA_DEV_ALLOCTOR_H
+
+struct usb_device;
+
+#ifdef CONFIG_MEDIA_CONTROLLER
+/**
+ * DOC: Media Controller Device Allocator API
+ *
+ * When media device belongs to more than one driver, the shared media device
+ * is allocated with the shared struct device as the key for look ups.
+ *
+ * Shared media device should stay in registered state until the last driver
+ * unregisters it. In addition, media device should be released when all the
+ * references are released. Each driver gets a reference to the media device
+ * during probe, when it allocates the media device. If media device is already
+ * allocated, allocate API bumps up the refcount and return the existing media
+ * device. Driver puts the reference back from its disconnect routine when it
+ * calls media_device_delete().
+ *
+ * Media device is unregistered and cleaned up from the kref put handler to
+ * ensure that the media device stays in registered state until the last driver
+ * unregisters the media device.
+ *
+ * Driver Usage:
+ *
+ * Drivers should use the media-core routines to get register reference and
+ * call media_device_delete() routine to make sure the shared media device
+ * delete is handled correctly.
+ *
+ * driver probe:
+ * Call media_device_usb_allocate() to allocate or get a reference
+ * Call media_device_register(), if media devnode isn't registered
+ *
+ * driver disconnect:
+ * Call media_device_delete() to free the media_device. Free'ing is
+ * handled by the put handler.
+ *
+ */
+
+/**
+ * media_device_usb_allocate() - Allocate and return media device
+ *
+ * @udev - struct usb_device pointer
+ * @module_name
+ *
+ * This interface should be called to allocate a media device when multiple
+ * drivers share usb_device and the media device. This interface allocates
+ * media device and calls media_device_usb_init() to initialize it.
+ *
+ */
+struct media_device *media_device_usb_allocate(struct usb_device *udev,
+ char *module_name);
+/**
+ * media_device_delete() - Release media device. Calls kref_put().
+ *
+ * @mdev - struct media_device pointer
+ * @module_name
+ *
+ * This interface should be called to put Media Device Instance kref.
+ */
+void media_device_delete(struct media_device *mdev, char *driver_name);
+#else
+static inline struct media_device *media_device_usb_allocate(
+ struct usb_device *udev, char *driver_name)
+ { return NULL; }
+static inline void media_device_delete(
+ struct media_device *mdev, char *module_name) { }
+#endif /* CONFIG_MEDIA_CONTROLLER */
+#endif
--
2.7.4
--
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