Re: [PATCH v2 2/2] V4L2: add CCF support to the v4l2_clk API

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Guennadi,

Thank you for the patch.

On Friday 02 January 2015 21:18:41 Guennadi Liakhovetski wrote:
> From aeaee56e04d023f3a019d2595ef5128015acdb06 Mon Sep 17 00:00:00 2001
> From: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> Date: Fri, 2 Jan 2015 12:26:41 +0100
> Subject: [PATCH 2/2] V4L2: add CCF support to the v4l2_clk API
> 
> V4L2 clocks, e.g. used by camera sensors for their master clock, do not
> have to be supplied by a different V4L2 driver, they can also be
> supplied by an independent source. In this case the standart kernel
> clock API should be used to handle such clocks. This patch adds support
> for such cases.
> 
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> ---
> 
> Hi Laurent,
> Thanks for the comment. The idea of allocating a new object for each "get"
> operation seems a bit weird to me, and completely trusting the user is a
> bit scary... :) But yes, it can work this way too, I think, and the user
> can screw either way too, anyway.

The user needs to get it right for when we'll replace v4l2_clk_get() with 
clk_get(), so I'd rather force it to get it right now.

> So, here comes a v2. Something like this?
> 
> v2: don't add CCF-related clocks on the global list, just allocate a new
> instance on each v4l2_clk_get()
> 
>  drivers/media/v4l2-core/v4l2-clk.c | 45 +++++++++++++++++++++++++++++++---
>  include/media/v4l2-clk.h           |  2 ++
>  2 files changed, 44 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-clk.c
> b/drivers/media/v4l2-core/v4l2-clk.c index c210906..f5d1688 100644
> --- a/drivers/media/v4l2-core/v4l2-clk.c
> +++ b/drivers/media/v4l2-core/v4l2-clk.c
> @@ -9,6 +9,7 @@
>   */
> 
>  #include <linux/atomic.h>
> +#include <linux/clk.h>
>  #include <linux/device.h>
>  #include <linux/errno.h>
>  #include <linux/list.h>
> @@ -42,6 +43,18 @@ static struct v4l2_clk *v4l2_clk_find(const char *dev_id,
> const char *id) struct v4l2_clk *v4l2_clk_get(struct device *dev, const
> char *id) {
>  	struct v4l2_clk *clk;
> +	struct clk *ccf_clk = clk_get(dev, id);
> +
> +	if (!IS_ERR(ccf_clk)) {
> +		clk = kzalloc(sizeof(struct v4l2_clk), GFP_KERNEL);
> +		if (!clk) {
> +			clk_put(ccf_clk);
> +			return ERR_PTR(-ENOMEM);
> +		}
> +		clk->clk = ccf_clk;
> +
> +		return clk;
> +	}

If clk_get() returns -EPROBE_DEFER I think you should return the error code to 
the user instead of falling back to the v4l2 clocks.

>  	mutex_lock(&clk_lock);
>  	clk = v4l2_clk_find(dev_name(dev), id);
> @@ -61,6 +74,12 @@ void v4l2_clk_put(struct v4l2_clk *clk)
>  	if (IS_ERR(clk))
>  		return;
> 
> +	if (clk->clk) {
> +		clk_put(clk->clk);
> +		kfree(clk);
> +		return;
> +	}
> +
>  	mutex_lock(&clk_lock);
> 
>  	list_for_each_entry(tmp, &clk_list, list)
> @@ -98,8 +117,12 @@ static void v4l2_clk_unlock_driver(struct v4l2_clk *clk)
> 
>  int v4l2_clk_enable(struct v4l2_clk *clk)
>  {
> -	int ret = v4l2_clk_lock_driver(clk);
> +	int ret;
> 
> +	if (clk->clk)
> +		return clk_enable(clk->clk);

Shouldn't you use clk_prepare_enable() ? CCF requires a prepare call before 
enabling the clock.

> +
> +	ret = v4l2_clk_lock_driver(clk);
>  	if (ret < 0)
>  		return ret;
> 
> @@ -125,6 +148,9 @@ void v4l2_clk_disable(struct v4l2_clk *clk)
>  {
>  	int enable;
> 
> +	if (clk->clk)
> +		return clk_disable(clk->clk);

Likewise, clk_disable_unprepare() ?

> +
>  	mutex_lock(&clk->lock);
> 
>  	enable = --clk->enable;
> @@ -142,8 +168,12 @@ EXPORT_SYMBOL(v4l2_clk_disable);
> 
>  unsigned long v4l2_clk_get_rate(struct v4l2_clk *clk)
>  {
> -	int ret = v4l2_clk_lock_driver(clk);
> +	int ret;
> +
> +	if (clk->clk)
> +		return clk_get_rate(clk->clk);
> 
> +	ret = v4l2_clk_lock_driver(clk);
>  	if (ret < 0)
>  		return ret;
> 
> @@ -162,7 +192,16 @@ EXPORT_SYMBOL(v4l2_clk_get_rate);
> 
>  int v4l2_clk_set_rate(struct v4l2_clk *clk, unsigned long rate)
>  {
> -	int ret = v4l2_clk_lock_driver(clk);
> +	int ret;
> +
> +	if (clk->clk) {
> +		long r = clk_round_rate(clk->clk, rate);
> +		if (r < 0)
> +			return r;
> +		return clk_set_rate(clk->clk, r);
> +	}
> +
> +	ret = v4l2_clk_lock_driver(clk);
> 
>  	if (ret < 0)
>  		return ret;
> diff --git a/include/media/v4l2-clk.h b/include/media/v4l2-clk.h
> index 8f06967..4402b2d 100644
> --- a/include/media/v4l2-clk.h
> +++ b/include/media/v4l2-clk.h
> @@ -22,6 +22,7 @@
>  struct module;
>  struct device;
> 
> +struct clk;
>  struct v4l2_clk {
>  	struct list_head list;
>  	const struct v4l2_clk_ops *ops;
> @@ -30,6 +31,7 @@ struct v4l2_clk {
>  	int enable;
>  	struct mutex lock; /* Protect the enable count */
>  	atomic_t use_count;
> +	struct clk *clk;
>  	void *priv;
>  };

-- 
Regards,

Laurent Pinchart