linux-kernel - Re: [PATCH v3 2/5] media: v4l2_ctrl: Add const pointer to ctrl

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Message-ID: <d08df115-f87d-947d-ca17-e9d82a077c9c@xs4all.nl>
Date:   Mon, 4 Nov 2019 10:48:17 +0100
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Ricardo Ribalda Delgado <ribalda@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] media: v4l2_ctrl: Add const pointer to ctrl_ptr

Hi Ricardo,

On 11/1/19 12:23 PM, Ricardo Ribalda Delgado wrote:
> This pointer is used to point to data that is constant. Thanks to this
> we can avoid a lot of casting and we make more clear when the data is
> constant or variable.
> 
> Suggested-by: Hans Verkuil <hverkuil-cisco@...all.nl>
> Signed-off-by: Ricardo Ribalda Delgado <ribalda@...nel.org>
> ---
>  include/media/v4l2-ctrls.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
> index 78a97b10c89e..7db9e719a583 100644
> --- a/include/media/v4l2-ctrls.h
> +++ b/include/media/v4l2-ctrls.h
> @@ -56,6 +56,7 @@ struct poll_table_struct;
>   * @p_hevc_slice_params:	Pointer to an HEVC slice parameters structure.
>   * @p_area:			Pointer to an area.
>   * @p:				Pointer to a compound value.
> + * @p_const:			Pointer to a constant compound value.
>   */
>  union v4l2_ctrl_ptr {
>  	s32 *p_s32;
> @@ -78,6 +79,7 @@ union v4l2_ctrl_ptr {
>  	struct v4l2_ctrl_hevc_slice_params *p_hevc_slice_params;
>  	struct v4l2_area *p_area;
>  	void *p;
> +	const void *p_const;
>  };
>  
>  /**
> 

This addition makes it possible to use const void pointers elsewhere in
the control framework.

E.g. in std_equal you can use p_const in the memcmp at the end.

Can you go through the v4l2-ctrls.c source and replace .p by .p_const
where it makes sense?

Obviously this would be a separate patch.

Regards,

	Hans