Re: [PATCH v2 1/6] media: add media token device resource framework

[Takashi Iwai]

At Tue, 14 Oct 2014 08:58:37 -0600,
Shuah Khan wrote:
> 
> Add media token device resource framework to allow sharing
> resources such as tuner, dma, audio etc. across media drivers
> and non-media sound drivers that control media hardware. The
> Media token resource is created at the main struct device that
> is common to all drivers that claim various pieces of the main
> media device, which allows them to find the resource using the
> main struct device. As an example, digital, analog, and
> snd-usb-audio drivers can use the media token resource API
> using the main struct device for the interface the media device
> is attached to.
> 
> A shared media tokens resource is created using devres framework
> for drivers to find and lock/unlock. Creating a shared devres
> helps avoid creating data structure dependencies between drivers.
> This media token resource contains media token for tuner, and
> audio. When tuner token is requested, audio token is issued.
> Subsequent token (for tuner and audio) gets from the same task
> and task in the same tgid succeed. This allows applications that
> make multiple v4l2 ioctls to work with the first call acquiring
> the token and applications that create separate threads to handle
> video and audio functions.
> 
> Signed-off-by: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
> ---
>  MAINTAINERS                  |    2 +
>  include/linux/media_tknres.h |   50 +++++++++
>  lib/Makefile                 |    2 +
>  lib/media_tknres.c           |  237 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 291 insertions(+)
>  create mode 100644 include/linux/media_tknres.h
>  create mode 100644 lib/media_tknres.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index e80a275..9216179 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -5864,6 +5864,8 @@ F:	include/uapi/linux/v4l2-*
>  F:	include/uapi/linux/meye.h
>  F:	include/uapi/linux/ivtv*
>  F:	include/uapi/linux/uvcvideo.h
> +F:	include/linux/media_tknres.h
> +F:	lib/media_tknres.c
>  
>  MEDIAVISION PRO MOVIE STUDIO DRIVER
>  M:	Hans Verkuil <hverkuil@xxxxxxxxx>
> diff --git a/include/linux/media_tknres.h b/include/linux/media_tknres.h
> new file mode 100644
> index 0000000..6d37327
> --- /dev/null
> +++ b/include/linux/media_tknres.h
> @@ -0,0 +1,50 @@
> +/*
> + * media_tknres.h - managed media token resource
> + *
> + * Copyright (c) 2014 Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
> + * Copyright (c) 2014 Samsung Electronics Co., Ltd.
> + *
> + * This file is released under the GPLv2.
> + */
> +#ifndef __LINUX_MEDIA_TOKEN_H
> +#define __LINUX_MEDIA_TOKEN_H
> +
> +struct device;
> +
> +#if defined(CONFIG_MEDIA_SUPPORT)
> +extern int media_tknres_create(struct device *dev);
> +extern int media_tknres_destroy(struct device *dev);
> +
> +extern int media_get_tuner_tkn(struct device *dev);
> +extern int media_put_tuner_tkn(struct device *dev);
> +
> +extern int media_get_audio_tkn(struct device *dev);
> +extern int media_put_audio_tkn(struct device *dev);

The words "tknres" and "tkn" (especially latter) look ugly and not
clear to me.  IMO, it should be "token".

> +#else
> +static inline int media_tknres_create(struct device *dev)
> +{
> +	return 0;
> +}
> +static inline int media_tknres_destroy(struct device *dev)
> +{
> +	return 0;
> +}
> +static inline int media_get_tuner_tkn(struct device *dev)
> +{
> +	return 0;
> +}
> +static inline int media_put_tuner_tkn(struct device *dev)
> +{
> +	return 0;
> +}
> +static int media_get_audio_tkn(struct device *dev)
> +{
> +	return 0;
> +}
> +static int media_put_audio_tkn(struct device *dev)
> +{
> +	return 0;
> +}
> +#endif
> +
> +#endif	/* __LINUX_MEDIA_TOKEN_H */
> diff --git a/lib/Makefile b/lib/Makefile
> index d6b4bc4..6f21695 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -139,6 +139,8 @@ obj-$(CONFIG_DQL) += dynamic_queue_limits.o
>  
>  obj-$(CONFIG_GLOB) += glob.o
>  
> +obj-$(CONFIG_MEDIA_SUPPORT) += media_tknres.o
> +
>  obj-$(CONFIG_MPILIB) += mpi/
>  obj-$(CONFIG_SIGNATURE) += digsig.o
>  
> diff --git a/lib/media_tknres.c b/lib/media_tknres.c
> new file mode 100644
> index 0000000..e0a36cb
> --- /dev/null
> +++ b/lib/media_tknres.c
> @@ -0,0 +1,237 @@
> +/*
> + * media_tknres.c - managed media token resource
> + *
> + * Copyright (c) 2014 Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
> + * Copyright (c) 2014 Samsung Electronics Co., Ltd.
> + *
> + * This file is released under the GPLv2.
> + */
> +/*
> + * Media devices often have hardware resources that are shared
> + * across several functions. For instance, TV tuner cards often
> + * have MUXes, converters, radios, tuners, etc. that are shared
> + * across various functions. However, v4l2, alsa, DVB, usbfs, and
> + * all other drivers have no knowledge of what resources are
> + * shared. For example, users can't access DVB and alsa at the same
> + * time, or the DVB and V4L analog API at the same time, since many
> + * only have one converter that can be in either analog or digital
> + * mode. Accessing and/or changing mode of a converter while it is
> + * in use by another function results in video stream error.
> + *
> + * A shared media tokens resource is created using devres framework
> + * for drivers to find and lock/unlock. Creating a shared devres
> + * helps avoid creating data structure dependencies between drivers.
> + * This media token resource contains media token for tuner, and
> + * audio. When tuner token is requested, audio token is issued.
> + * Subsequent token (for tuner and audio) gets from the same task
> + * and task in the same tgid succeed. This allows applications that
> + * make multiple v4l2 ioctls to work with the first call acquiring
> + * the token and applications that create separate threads to handle
> + * video and audio functions.
> + *
> + * API
> + *	int media_tknres_create(struct device *dev);
> + *	int media_tknres_destroy(struct device *dev);
> + *
> + *	int media_get_tuner_tkn(struct device *dev);
> + *	int media_put_tuner_tkn(struct device *dev);
> + *
> + *	int media_get_audio_tkn(struct device *dev);
> + *	int media_put_audio_tkn(struct device *dev);
> +*/
> +
> +#include <linux/kernel.h>
> +#include <linux/device.h>
> +#include <linux/sched.h>
> +#include <linux/media_tknres.h>
> +
> +struct media_tkn {
> +	spinlock_t lock;
> +	unsigned int owner;	/* owner task pid */
> +	unsigned int tgid;	/* owner task gid */
> +	struct task_struct *task;
> +};
> +
> +struct media_tknres {
> +	struct media_tkn tuner;
> +	struct media_tkn audio;
> +};

Why do you need to have both tuner and audio tokens?  If I understand
correctly, no matter whether it's tuner or audio, if it's being used,
the open must fail, right?

> +
> +#define TUNER	"Tuner"
> +#define AUDIO	"Audio"
> +
> +static void media_tknres_release(struct device *dev, void *res)
> +{
> +	dev_info(dev, "%s: Media Token Resource released\n", __func__);
> +}
> +
> +int media_tknres_create(struct device *dev)
> +{
> +	struct media_tknres *tkn;
> +
> +	tkn = devres_alloc(media_tknres_release, sizeof(struct media_tknres),
> +				GFP_KERNEL);
> +	if (!tkn)
> +		return -ENOMEM;
> +
> +	spin_lock_init(&tkn->tuner.lock);
> +	tkn->tuner.owner = 0;
> +	tkn->tuner.tgid = 0;
> +	tkn->tuner.task = NULL;
> +
> +	spin_lock_init(&tkn->audio.lock);
> +	tkn->audio.owner = 0;
> +	tkn->audio.tgid = 0;
> +	tkn->audio.task = NULL;
> +
> +	devres_add(dev, tkn);
> +
> +	dev_info(dev, "%s: Media Token Resource created\n", __func__);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(media_tknres_create);
> +
> +static int __media_get_tkn(struct media_tkn *tkn, char *tkn_str)
> +{
> +	int rc = 0;
> +	unsigned tpid;
> +	unsigned tgid;
> +
> +	spin_lock(&tkn->lock);

You should use spin_lock_irqsave() here and in all other places.
The trigger callback in usb-audio, for example, may be called in irq
context.

> +
> +	tpid = task_pid_nr(current);
> +	tgid = task_tgid_nr(current);
> +
> +	/* allow task in the same group id to release */

IMO, it's not "release" but "steal"...  But what happens if the stolen
owner calls put?  Then it'll be released although the stealing owner
still thinks it's being held.

> +	if (tkn->task && ((tkn->task != current) && (tkn->tgid != tgid))) {

Shouldn't the second "&&" be "||" instead?
And too many parentheses there.

> +			rc = -EBUSY;

Wrong indentation.

I have a feeling that the whole thing can be a bit more simplified in
the end...


thanks,

Takashi

> +	} else {
> +		tkn->owner = tpid;
> +		tkn->tgid = tgid;
> +		tkn->task = current;
> +	}
> +	pr_debug("%s: Media %s Token get: owner (%d,%d) req (%d,%d) rc %d\n",
> +		__func__, tkn_str, tkn->owner, tkn->tgid, tpid, tgid, rc);
> +
> +	spin_unlock(&tkn->lock);
> +	return rc;
> +}
> +
> +static int __media_put_tkn(struct media_tkn *tkn, char *tkn_str)
> +{
> +	int rc = 0;
> +	unsigned tpid;
> +	unsigned tgid;
> +
> +	spin_lock(&tkn->lock);
> +
> +	tpid = task_pid_nr(current);
> +	tgid = task_tgid_nr(current);
> +
> +	/* allow task in the same group id to release */
> +	if (tkn->task == NULL ||
> +		((tkn->task != current) && (tkn->tgid != tgid))) {
> +			rc = -EINVAL;
> +	} else {
> +		tkn->owner = 0;
> +		tkn->tgid = 0;
> +		tkn->task = NULL;
> +	}
> +	pr_debug("%s: Media %s Token put: owner (%d,%d) req (%d,%d) rc %d\n",
> +		__func__, tkn_str, tkn->owner, tkn->tgid, tpid, tgid, rc);
> +
> +	spin_unlock(&tkn->lock);
> +	return rc;
> +}
> +
> +/*
> + * When media tknres doesn't exist, get and put interfaces
> + * return 0 to let the callers take legacy code paths. This
> + * will also cover the drivers that don't create media tknres.
> + * Returning -ENODEV will require additional checks by callers.
> + * Instead handle the media tknres not present case as a driver
> + * not supporting media tknres and return 0.
> +*/
> +int media_get_tuner_tkn(struct device *dev)
> +{
> +	struct media_tknres *tkn_ptr;
> +	int ret = 0;
> +
> +	tkn_ptr = devres_find(dev, media_tknres_release, NULL, NULL);
> +	if (tkn_ptr == NULL) {
> +		dev_dbg(dev, "%s: Media Token Resource not found\n",
> +				__func__);
> +		return 0;
> +	}
> +
> +	ret = __media_get_tkn(&tkn_ptr->tuner, TUNER);
> +	if (ret)
> +		return ret;
> +
> +	/* get audio token */
> +	ret = __media_get_tkn(&tkn_ptr->audio, AUDIO);
> +	if (ret)
> +		__media_put_tkn(&tkn_ptr->tuner, TUNER);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(media_get_tuner_tkn);
> +
> +int media_put_tuner_tkn(struct device *dev)
> +{
> +	struct media_tknres *tkn_ptr;
> +
> +	tkn_ptr = devres_find(dev, media_tknres_release, NULL, NULL);
> +	if (tkn_ptr == NULL) {
> +		dev_dbg(dev, "%s: Media Token Resource not found\n",
> +			__func__);
> +		return 0;
> +	}
> +
> +	/* put audio token and then tuner token */
> +	__media_put_tkn(&tkn_ptr->audio, AUDIO);
> +
> +	return __media_put_tkn(&tkn_ptr->tuner, TUNER);
> +}
> +EXPORT_SYMBOL_GPL(media_put_tuner_tkn);
> +
> +int media_get_audio_tkn(struct device *dev)
> +{
> +	struct media_tknres *tkn_ptr;
> +
> +	tkn_ptr = devres_find(dev, media_tknres_release, NULL, NULL);
> +	if (tkn_ptr == NULL) {
> +		dev_dbg(dev, "%s: Media Token Resource not found\n",
> +			__func__);
> +		return 0;
> +	}
> +
> +	return __media_get_tkn(&tkn_ptr->audio, AUDIO);
> +}
> +EXPORT_SYMBOL_GPL(media_get_audio_tkn);
> +
> +int media_put_audio_tkn(struct device *dev)
> +{
> +	struct media_tknres *tkn_ptr;
> +
> +	tkn_ptr = devres_find(dev, media_tknres_release, NULL, NULL);
> +	if (tkn_ptr == NULL) {
> +		dev_dbg(dev, "%s: Media Token Resource not found\n",
> +			__func__);
> +		return 0;
> +	}
> +
> +	return __media_put_tkn(&tkn_ptr->audio, AUDIO);
> +}
> +EXPORT_SYMBOL_GPL(media_put_audio_tkn);
> +
> +int media_tknres_destroy(struct device *dev)
> +{
> +	int rc;
> +
> +	rc = devres_release(dev, media_tknres_release, NULL, NULL);
> +	WARN_ON(rc);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(media_tknres_destroy);
> -- 
> 1.7.10.4
> 
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