linux-kernel - Re: [PATCH 3/8] media/v4l2-core: struct struct v4l2_ext

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Date:	Fri, 21 Aug 2015 12:11:16 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Mike Isely <isely@...ox.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Steven Toth <stoth@...nellabs.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Vincent Palatin <vpalatin@...omium.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] media/v4l2-core: struct struct v4l2_ext_controls
 param which

On 08/21/2015 11:29 AM, Ricardo Ribalda Delgado wrote:
> Support for new field which on v4l2_ext_controls, used to get the
> default value of one or more controls.
> 
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> ---
>  drivers/media/v4l2-core/v4l2-ctrls.c | 35 ++++++++++++++++++++++++++++++-----
>  1 file changed, 30 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index b6b7dcc1b77d..23a69f637f6d 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -1489,6 +1489,17 @@ static int new_to_user(struct v4l2_ext_control *c,
>  	return ptr_to_user(c, ctrl, ctrl->p_new);
>  }
>  
> +/* Helper function: copy the initial control value back to the caller */
> +static int def_to_user(struct v4l2_ext_control *c, struct v4l2_ctrl *ctrl)
> +{
> +	int idx;
> +
> +	for (idx = 0; idx < ctrl->elems; idx++)
> +		ctrl->type_ops->init(ctrl, idx, ctrl->p_new);
> +
> +	return ptr_to_user(c, ctrl, ctrl->p_new);
> +}
> +
>  /* Helper function: copy the caller-provider value to the given control value */
>  static int user_to_ptr(struct v4l2_ext_control *c,
>  		       struct v4l2_ctrl *ctrl,
> @@ -2708,7 +2719,9 @@ static int prepare_ext_ctrls(struct v4l2_ctrl_handler *hdl,
>  
>  		cs->error_idx = i;
>  
> -		if (cs->ctrl_class && V4L2_CTRL_ID2CLASS(id) != cs->ctrl_class)
> +		if (cs->ctrl_class &&
> +		    cs->which != V4L2_CTRL_WHICH_DEF_VAL &&
> +		    V4L2_CTRL_ID2CLASS(id) != cs->ctrl_class)
>  			return -EINVAL;
>  
>  		/* Old-style private controls are not allowed for
> @@ -2787,7 +2800,7 @@ static int prepare_ext_ctrls(struct v4l2_ctrl_handler *hdl,
>     whether there are any controls at all. */
>  static int class_check(struct v4l2_ctrl_handler *hdl, u32 ctrl_class)
>  {
> -	if (ctrl_class == 0)
> +	if (ctrl_class == 0 || ctrl_class == V4L2_CTRL_WHICH_DEF_VAL)
>  		return list_empty(&hdl->ctrl_refs) ? -EINVAL : 0;
>  	return find_ref_lock(hdl, ctrl_class | 1) ? 0 : -EINVAL;
>  }
> @@ -2801,10 +2814,14 @@ int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct v4l2_ext_controls *cs
>  	struct v4l2_ctrl_helper *helpers = helper;
>  	int ret;
>  	int i, j;
> +	bool def_value = false;
>  
>  	cs->error_idx = cs->count;
>  	cs->ctrl_class = V4L2_CTRL_ID2CLASS(cs->ctrl_class);
>  
> +	if (cs->which == V4L2_CTRL_WHICH_DEF_VAL)
> +		def_value = true;
> +

Ah, this is confusing. First assigning to ctrl_class, then checking 'which'.

I would add a patch after patch 2/8 that replaces all occurrences of ctrl_class in
by 'which'. It's only used in v4l2-core, the saa7164 driver and in Documentation.
The old 'ctrl_class' shouldn't be used in the kernel anymore.

It is probably a good idea to put #ifndef __KERNEL__ around the ctrl_class field in
the header. That way it isn't visible in the kernel at all.

I would also rename V4L2_CTRL_ID2CLASS to V4L2_CTRL_ID2WHICH (and keep the old define
as #define V4L2_CTRL_ID2CLASS V4L2_CTRL_ID2WHICH under #ifndef __KERNEL__).

>  	if (hdl == NULL)
>  		return -EINVAL;
>  
> @@ -2827,9 +2844,11 @@ int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct v4l2_ext_controls *cs
>  
>  	for (i = 0; !ret && i < cs->count; i++) {
>  		int (*ctrl_to_user)(struct v4l2_ext_control *c,
> -				    struct v4l2_ctrl *ctrl) = cur_to_user;
> +				    struct v4l2_ctrl *ctrl);
>  		struct v4l2_ctrl *master;
>  
> +		ctrl_to_user = def_value ? def_to_user : cur_to_user;
> +
>  		if (helpers[i].mref == NULL)
>  			continue;
>  
> @@ -2839,8 +2858,9 @@ int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct v4l2_ext_controls *cs
>  		v4l2_ctrl_lock(master);
>  
>  		/* g_volatile_ctrl will update the new control values */
> -		if ((master->flags & V4L2_CTRL_FLAG_VOLATILE) ||
> -			(master->has_volatiles && !is_cur_manual(master))) {
> +		if (!def_value &&
> +		    ((master->flags & V4L2_CTRL_FLAG_VOLATILE) ||
> +		    (master->has_volatiles && !is_cur_manual(master)))) {
>  			for (j = 0; j < master->ncontrols; j++)
>  				cur_to_new(master->cluster[j]);
>  			ret = call_op(master, g_volatile_ctrl);
> @@ -3062,6 +3082,11 @@ static int try_set_ext_ctrls(struct v4l2_fh *fh, struct v4l2_ctrl_handler *hdl,
>  	int ret;
>  
>  	cs->error_idx = cs->count;
> +
> +	/* Default value cannot be changed */
> +	if (cs->which == V4L2_CTRL_WHICH_DEF_VAL)
> +		return -EINVAL;
> +
>  	cs->ctrl_class = V4L2_CTRL_ID2CLASS(cs->ctrl_class);
>  
>  	if (hdl == NULL)
> 

Regards,

	Hans
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