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

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Linux Media Mailing List <linux-media@vger.kernel.org>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	Sylwester Nawrocki <s.nawrocki@samsung.com>,
	Sylwester Nawrocki <sylvester.nawrocki@gmail.com>,
	Magnus Damm <magnus.damm@gmail.com>,
	linux-sh@vger.kernel.org
Subject: Re: [PATCH 1/2] media: V4L2: add temporary clock helpers
Date: Mon, 22 Oct 2012 12:55:33 +0000	[thread overview]
Message-ID: <10639536.MyZHsyuauD@avalon> (raw)
In-Reply-To: <Pine.LNX.4.64.1210200007310.28993@axis700.grange>

Hi Guennadi,

Thanks for the patch. Here are a few comments in addition to what Sylwester 
already mentioned.

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;
> +	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);
> +}
> +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;

What about kstrdup() ing name and dev_name here ? Otherwise callers would need 
to make sure that names are not stored in temporary locations (on the stack 
for instance), leading to possibly difficult to debug crashes.

We would then need a priv field in struct v4l2_clk/

> +
> +	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;

You should forward-declare struct v4l2_clk_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