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Date: Fri, 27 May 2016 15:26:41 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Shuah Khan <shuahkh@....samsung.com>, mchehab@....samsung.com,
laurent.pinchart@...asonboard.com, sakari.ailus@....fi,
hans.verkuil@...co.com, chehabrafael@...il.com,
javier@....samsung.com, inki.dae@...sung.com,
g.liakhovetski@....de, jh1009.sung@...sung.com
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] media: Media Device Allocator API
On 05/25/2016 01:39 AM, Shuah Khan wrote:
> 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@....samsung.com>
> ---
> drivers/media/Makefile | 3 +-
> drivers/media/media-dev-allocator.c | 120 ++++++++++++++++++++++++++++++++++++
> include/media/media-dev-allocator.h | 85 +++++++++++++++++++++++++
> 3 files changed, 207 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 e608bbc..b08f091 100644
> --- a/drivers/media/Makefile
> +++ b/drivers/media/Makefile
> @@ -2,7 +2,8 @@
> # 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
>
> #
> # 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..b8c9811
> --- /dev/null
> +++ b/drivers/media/media-dev-allocator.c
> @@ -0,0 +1,120 @@
> +/*
> + * media-dev-allocator.c - Media Controller Device Allocator API
> + *
> + * Copyright (c) 2016 Shuah Khan <shuahkh@....samsung.com>
> + * Copyright (c) 2016 Samsung Electronics Co., Ltd.
> + *
> + * This file is released under the GPLv2.
> + * Credits: Suggested by Laurent Pinchart <laurent.pinchart@...asonboard.com>
> + */
> +
> +/*
> + * 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 <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 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);
> +}
> +
Add a comment here saying that media_device_lock has to be locked when
calling this get function.
> +static struct media_device *__media_device_get(struct device *dev,
> + bool allocate)
I think you can just drop the allocate argument: you're always allocating if
the media_device wasn't found.
> +{
> + struct media_device_instance *mdi;
> +
> + list_for_each_entry(mdi, &media_device_list, list) {
> + if (mdi->dev == dev) {
> + kref_get(&mdi->refcount);
> + dev_dbg(dev, "%s: get mdev=%p\n",
> + __func__, &mdi->mdev);
> + goto done;
Just say 'return &mdi->mdev;', no goto needed.
> + }
> + }
> +
> + if (!allocate) {
> + mdi = NULL;
> + goto done;
> + }
> +
> + mdi = kzalloc(sizeof(*mdi), GFP_KERNEL);
> + if (!mdi)
> + goto done;
Same here, just do 'return NULL;'
> +
> + mdi->dev = dev;
> + kref_init(&mdi->refcount);
> + list_add_tail(&mdi->list, &media_device_list);
> +
> + dev_dbg(dev, "%s: alloc mdev=%p\n", __func__, &mdi->mdev);
> +done:
> + return mdi ? &mdi->mdev : NULL;
> +}
> +
> +struct media_device *media_device_usb_allocate(struct usb_device *udev,
> + char *driver_name)
> +{
> + struct media_device *mdev;
> +
> + mutex_lock(&media_device_lock);
> + mdev = __media_device_get(&udev->dev, true);
> + 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,
> + driver_name);
> + mutex_unlock(&media_device_lock);
> +
> + dev_dbg(&udev->dev, "%s\n", __func__);
> + return mdev;
> +}
> +EXPORT_SYMBOL_GPL(media_device_usb_allocate);
> +
> +void media_device_delete(struct media_device *mdev)
> +{
> + struct media_device_instance *mdi = to_media_device_instance(mdev);
> +
> + dev_dbg(mdi->mdev.dev, "%s: mdev=%p\n", __func__, &mdi->mdev);
> + 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..fda032b
> --- /dev/null
> +++ b/include/media/media-dev-allocator.h
> @@ -0,0 +1,85 @@
> +/*
> + * media-dev-allocator.h - Media Controller Device Allocator API
> + *
> + * Copyright (c) 2016 Shuah Khan <shuahkh@....samsung.com>
> + * Copyright (c) 2016 Samsung Electronics Co., Ltd.
> + *
> + * This file is released under the GPLv2.
> + * Credits: Suggested by Laurent Pinchart <laurent.pinchart@...asonboard.com>
> + */
> +
> +/*
> + * 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
> + * @driver_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 *driver_name);
> +/**
> + * media_device_delete() - Release media device. Calls kref_put().
> + *
> + * @mdev - struct media_device pointer
> + *
> + * This interface should be called to put Media Device Instance kref.
> + */
> +void media_device_delete(struct media_device *mdev);
> +#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) { }
> +#endif /* CONFIG_MEDIA_CONTROLLER */
> +#endif
>
Regards,
Hans
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