Re: [PATCH 1/2] media: V4L2: add temporary clock helpers

Laurent Pinchart
2012-10-22T12:58:14Z

Hi Guennadi,

A couple more comments.

On Saturday 20 October 2012 00:20:20 Guennadi Liakhovetski wrote:
> Typical video devices like camera sensors require an external clock source.
> Many such devices cannot even access their hardware registers without a
> running clock. These clock sources should be controlled by their consumers.
> This should be performed, using the generic clock framework. Unfortunately
> so far only very few systems have been ported to that framework. This patch
> adds a set of temporary helpers, mimicking the generic clock API, to V4L2.
> Platforms, adopting the clock API, should switch to using it. Eventually
> this temporary API should be removed.
>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> ---
> drivers/media/v4l2-core/Makefile | 2 +-
> drivers/media/v4l2-core/v4l2-clk.c | 126 +++++++++++++++++++++++++++++++++
> include/media/v4l2-clk.h | 48 ++++++++++++++
> 3 files changed, 175 insertions(+), 1 deletions(-)
> create mode 100644 drivers/media/v4l2-core/v4l2-clk.c
> create mode 100644 include/media/v4l2-clk.h
>
> diff --git a/drivers/media/v4l2-core/Makefile
> b/drivers/media/v4l2-core/Makefile index 00f64d6..cb5fede 100644
> --- a/drivers/media/v4l2-core/Makefile
> +++ b/drivers/media/v4l2-core/Makefile
> @@ -5,7 +5,7 @@
> tuner-objs := tuner-core.o
>
> videodev-objs := v4l2-dev.o v4l2-ioctl.o v4l2-device.o v4l2-fh.o \
> - v4l2-event.o v4l2-ctrls.o v4l2-subdev.o
> + v4l2-event.o v4l2-ctrls.o v4l2-subdev.o v4l2-clk.o
> ifeq ($(CONFIG_COMPAT),y)
> videodev-objs += v4l2-compat-ioctl32.o
> endif
> diff --git a/drivers/media/v4l2-core/v4l2-clk.c
> b/drivers/media/v4l2-core/v4l2-clk.c new file mode 100644
> index 0000000..7d457e4
> --- /dev/null
> +++ b/drivers/media/v4l2-core/v4l2-clk.c
> @@ -0,0 +1,126 @@
> +/*
> + * V4L2 clock service
> + *
> + * Copyright (C) 2012, Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/string.h>
> +
> +#include <media/v4l2-clk.h>
> +#include <media/v4l2-subdev.h>
> +
> +static DEFINE_MUTEX(clk_lock);
> +static LIST_HEAD(v4l2_clk);
> +
> +struct v4l2_clk *v4l2_clk_get(struct v4l2_subdev *sd, const char *id)
> +{
> + struct v4l2_clk *clk = NULL;
> +
> + mutex_lock(&clk_lock);
> + if (!id) {
> + if (list_is_singular(&v4l2_clk)) {
> + clk = list_entry(&v4l2_clk, struct v4l2_clk, list);
> + if (!strstr(sd->name, clk->dev_id))
> + clk = ERR_PTR(-ENODEV);
> + } else {
> + clk = ERR_PTR(-EINVAL);
> + }
> + } else {
> + list_for_each_entry(clk, &v4l2_clk, list) {
> + if (!strcmp(id, clk->id) &&
> + !strcmp(sd->name, clk->dev_id))
> + break;
> + }
> + if (&clk->list == &v4l2_clk)
> + clk = ERR_PTR(-ENODEV);
> + }
> + mutex_unlock(&clk_lock);
> +
> + if (!IS_ERR(clk) &&
> + !try_module_get(clk->ops->owner))
> + clk = ERR_PTR(-ENODEV);
> +
> + return clk;
> +}
> +EXPORT_SYMBOL(v4l2_clk_get);
> +
> +void v4l2_clk_put(struct v4l2_clk *clk)
> +{
> + if (!IS_ERR(clk))
> + module_put(clk->ops->owner);
> +}
> +EXPORT_SYMBOL(v4l2_clk_put);
> +
> +int v4l2_clk_enable(struct v4l2_clk *clk)
> +{
> + if (!clk->ops->enable)
> + return -ENOSYS;

Are enable/disable supposed to be refcounted ? What about adding the refcount
(or a boolean enable field) to struct v4l2_clk and handling it here and in
v4l2_clk_disable() ?

> + return clk->ops->enable(clk);
> +}
> +EXPORT_SYMBOL(v4l2_clk_enable);
> +
> +void v4l2_clk_disable(struct v4l2_clk *clk)
> +{
> + if (clk->ops->disable)
> + clk->ops->disable(clk);
> +}
> +EXPORT_SYMBOL(v4l2_clk_disable);
> +
> +unsigned long v4l2_clk_get_rate(struct v4l2_clk *clk)
> +{
> + if (!clk->ops->get_rate)
> + return -ENOSYS;
> + return clk->ops->get_rate(clk);
> +}
> +EXPORT_SYMBOL(v4l2_clk_get_rate);
> +
> +int v4l2_clk_set_rate(struct v4l2_clk *clk, unsigned long rate)
> +{
> + if (!clk->ops->set_rate)
> + return -ENOSYS;
> + return clk->ops->set_rate(clk, rate);

What's the expected behaviour when calling v4l2_clk_get/set_rate on a disabled
clock ?

> +}
> +EXPORT_SYMBOL(v4l2_clk_set_rate);
> +
> +struct v4l2_clk *v4l2_clk_register(const struct v4l2_clk_ops *ops,
> + const char *dev_name,
> + const char *name)
> +{
> + struct v4l2_clk *clk;
> +
> + if (!ops || !ops->owner || (!list_empty(&v4l2_clk) && !name))
> + return ERR_PTR(-EINVAL);
> +
> + clk = kzalloc(sizeof(struct v4l2_clk), GFP_KERNEL);
> + if (!clk)
> + return ERR_PTR(-ENOMEM);
> +
> + clk->ops = ops;
> + clk->id = name;
> + clk->dev_id = dev_name;
> +
> + mutex_lock(&clk_lock);
> + list_add_tail(&clk->list, &v4l2_clk);
> + mutex_unlock(&clk_lock);
> +
> + return clk;
> +}
> +EXPORT_SYMBOL(v4l2_clk_register);
> +
> +void v4l2_clk_unregister(struct v4l2_clk *clk)
> +{
> + mutex_lock(&clk_lock);
> + list_del(&clk->list);
> + mutex_unlock(&clk_lock);
> +
> + kfree(clk);
> +}
> +EXPORT_SYMBOL(v4l2_clk_unregister);
> diff --git a/include/media/v4l2-clk.h b/include/media/v4l2-clk.h
> new file mode 100644
> index 0000000..0c05ab3
> --- /dev/null
> +++ b/include/media/v4l2-clk.h
> @@ -0,0 +1,48 @@
> +/*
> + * V4L2 clock service
> + *
> + * Copyright (C) 2012, Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * ATTENTION: This is a temporary API and it shall be replaced by the
> generic + * clock API, when the latter becomes widely available.
> + */
> +
> +#ifndef MEDIA_V4L2_CLK_H
> +#define MEDIA_V4L2_CLK_H
> +
> +#include <linux/list.h>
> +
> +struct module;
> +struct v4l2_subdev;
> +
> +struct v4l2_clk {
> + struct list_head list;
> + const struct v4l2_clk_ops *ops;
> + const char *dev_id;
> + const char *id;
> +};
> +
> +struct v4l2_clk_ops {
> + struct module *owner;
> + int (*enable)(struct v4l2_clk *clk);
> + void (*disable)(struct v4l2_clk *clk);
> + unsigned long (*get_rate)(struct v4l2_clk *clk);
> + int (*set_rate)(struct v4l2_clk *clk, unsigned long);
> +};
> +
> +struct v4l2_clk *v4l2_clk_register(const struct v4l2_clk_ops *ops,
> + const char *dev_name,
> + const char *name);
> +void v4l2_clk_unregister(struct v4l2_clk *clk);
> +struct v4l2_clk *v4l2_clk_get(struct v4l2_subdev *sd, const char *id);
> +void v4l2_clk_put(struct v4l2_clk *clk);
> +int v4l2_clk_enable(struct v4l2_clk *clk);
> +void v4l2_clk_disable(struct v4l2_clk *clk);
> +unsigned long v4l2_clk_get_rate(struct v4l2_clk *clk);
> +int v4l2_clk_set_rate(struct v4l2_clk *clk, unsigned long rate);
> +
> +#endif
--
Regards,

Laurent Pinchart