Re: [RFC PATCH v8 1/4] media: Media Device Allocator API
From: shuah
Date: Thu Dec 06 2018 - 10:27:59 EST
Hi Hans,
On 11/20/18 4:20 AM, Hans Verkuil wrote:
On 11/02/2018 01:31 AM, shuah@xxxxxxxxxx wrote:
From: Shuah Khan <shuah@xxxxxxxxxx>
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 <shuah@xxxxxxxxxx>
Thanks for catching the documentation corrections. Fixed them all and
working on the next revision of the patch.
---
Documentation/media/kapi/mc-core.rst | 37 ++++++++
drivers/media/Makefile | 3 +-
drivers/media/media-dev-allocator.c | 132 +++++++++++++++++++++++++++
include/media/media-dev-allocator.h | 53 +++++++++++
4 files changed, 224 insertions(+), 1 deletion(-)
create mode 100644 drivers/media/media-dev-allocator.c
create mode 100644 include/media/media-dev-allocator.h
diff --git a/Documentation/media/kapi/mc-core.rst b/Documentation/media/kapi/mc-core.rst
index 0c05503eaf1f..d6f409598065 100644
--- a/Documentation/media/kapi/mc-core.rst
+++ b/Documentation/media/kapi/mc-core.rst
@@ -257,8 +257,45 @@ Subsystems should facilitate link validation by providing subsystem specific
helper functions to provide easy access for commonly needed information, and
in the end provide a way to use driver-specific callbacks.
+Media Controller Device Allocator API
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When media device belongs to more than one driver, the shared media device
When -> When the
+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
Shared -> The shared
+unregisters it. In addition, media device should be released when all the
media -> the media
+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
allocate -> the allocate
return -> returns
+device. Driver puts the reference back from its disconnect routine when it
Driver -> The driver
from -> in
+calls :c:func:`media_device_delete()`.
+
+Media device is unregistered and cleaned up from the kref put handler to
Media -> The media
from -> in
+ensure that the media device stays in registered state until the last driver
+unregisters the media device.
What happens if an application still has the media device open and you forcibly
remove the last driver? I think it should be OK since the media_devnode struct
isn't freed until the last open filehandle closes. But it is good to test this.
+
+**Driver Usage**
+
+Drivers should use the media-core routines to get register reference and
'get register reference'? Not sure what you meant to say.
+call :c:func:`media_device_delete()` routine to make sure the shared media
+device delete is handled correctly.
+
+**driver probe:**
+Call :c:func:`media_device_usb_allocate()` to allocate or get a reference
+Call :c:func:`media_device_register()`, if media devnode isn't registered
+
+**driver disconnect:**
+Call :c:func:`media_device_delete()` to free the media_device. Free'ing is
Free'ing -> Freeing
+handled by the kref put handler.
+
+API Definitions
+^^^^^^^^^^^^^^^
+
.. kernel-doc:: include/media/media-device.h
.. kernel-doc:: include/media/media-devnode.h
.. kernel-doc:: include/media/media-entity.h
+
+.. kernel-doc:: include/media/media-dev-allocator.h
diff --git a/drivers/media/Makefile b/drivers/media/Makefile
index 594b462ddf0e..8608f0a41dca 100644
--- a/drivers/media/Makefile
+++ b/drivers/media/Makefile
@@ -3,7 +3,8 @@
# Makefile for the kernel multimedia device drivers.
#
-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
Perhaps only add media-dev-allocator if CONFIG_USB is enabled?
#
# 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 000000000000..262d1293dc13
--- /dev/null
+++ b/drivers/media/media-dev-allocator.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * media-dev-allocator.c - Media Controller Device Allocator API
+ *
+ * Copyright (c) 2018 Shuah Khan <shuah@xxxxxxxxxx>
+ *
+ * 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/kref.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/usb.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 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);
Can't the lock be moved down to just before list_del? Or am I missing something?
The lock needs to be held while media_device_unregister() and
media_device_cleanup() to avoid races in the unregister path if two
drivers call media_device_delete().
+
+ 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)
const char *
Thanks fixed all of these.
I am running final tests and will send the next version this week.
thanks,
-- Shuah