linux-kernel - Re: [PATCH v8 7/8] media: v4l2-ctrl: Add new helper v4l2_ctrl_ptr_from

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Date:   Mon, 30 Sep 2019 15:05:08 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Ricardo Ribalda Delgado <ribalda@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jacopo Mondi <jacopo@...ndi.org>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Hans Verkuil <hverkuil@...all.nl>
Subject: Re: [PATCH v8 7/8] media: v4l2-ctrl: Add new helper
 v4l2_ctrl_ptr_from_void

On 9/30/19 12:18 PM, Ricardo Ribalda Delgado wrote:
> This helper function simplifies the code by not needing a union
> v4l2_ctrl_ptr and an assignment every time we need to use
> a ctrl_ptr.
> 
> Suggested-by: Hans Verkuil <hverkuil@...all.nl>
> Signed-off-by: Ricardo Ribalda Delgado <ribalda@...nel.org>
> ---
>  include/media/v4l2-ctrls.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
> index c42f164e2c9e..d69cfdffd41d 100644
> --- a/include/media/v4l2-ctrls.h
> +++ b/include/media/v4l2-ctrls.h
> @@ -73,6 +73,17 @@ union v4l2_ctrl_ptr {
>  	void *p;
>  };
>  
> +/**
> + * v4l2_ctrl_ptr() - Helper function to return a v4l2_ctrl_ptr from a
> + * void pointer
> + * @ptr:	The void pointer
> + */
> +static inline union v4l2_ctrl_ptr v4l2_ctrl_ptr_from_void(void *ptr)
> +{
> +	BUILD_BUG_ON(sizeof(union v4l2_ctrl_ptr) != sizeof(void *));
> +	return (union v4l2_ctrl_ptr) ptr;

Huh? Why not just do:

	union v4l2_ctrl_ptr p = { .p = ptr; };

	return p;

Or even shorter (not tested): return (union v4l2_ctrl_ptr) { .p = ptr; };

No need for BUILD_BUG_ON that way, which is rather ugly.

Regards,

	Hans

> +}
> +
>  /**
>   * struct v4l2_ctrl_ops - The control operations that the driver has to provide.
>   *
>