linux-kernel - Re: [PATCH v2 04/10] media: v4l2-dev: Add helpers to get current format from the state

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Message-ID: <f2178b2d-d8ea-470f-8f8f-8ffc0380cee5@kernel.org>
Date: Mon, 22 Sep 2025 10:06:59 +0200
From: Hans Verkuil <hverkuil+cisco@...nel.org>
To: Jai Luthra <jai.luthra@...asonboard.com>,
 Hans Verkuil <hverkuil@...nel.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Jacopo Mondi <jacopo.mondi@...asonboard.com>, linux-media@...r.kernel.org
Cc: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
 Ma Ke <make24@...as.ac.cn>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 04/10] media: v4l2-dev: Add helpers to get current
 format from the state

On 19/09/2025 11:55, Jai Luthra wrote:
> Add a helper function that drivers can call to retrieve the current
> v4l2_format stored in a video device state for internal use.
> 
> Additionally, provide a G_FMT ioctl implementation that drivers can use
> instead of writing their own when the format is stored in the active
> state.
> 
> Signed-off-by: Jai Luthra <jai.luthra@...asonboard.com>
> --
> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> Cc: Hans Verkuil <hverkuil@...nel.org>
> Cc: Jai Luthra <jai.luthra@...asonboard.com>
> Cc: Ricardo Ribalda <ribalda@...omium.org>
> Cc: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> Cc: Ma Ke <make24@...as.ac.cn>
> Cc: linux-media@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/media/v4l2-core/v4l2-dev.c | 23 +++++++++++++++++++++++
>  include/media/v4l2-dev.h           | 18 ++++++++++++++++++
>  2 files changed, 41 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> index dff23c6a0b56fb3d29e1c04e386bb445fa8773bb..2606077538be0e83032c6ae8956c1d67da0d0c5d 100644
> --- a/drivers/media/v4l2-core/v4l2-dev.c
> +++ b/drivers/media/v4l2-core/v4l2-dev.c
> @@ -199,6 +199,29 @@ void __video_device_state_free(struct video_device_state *state)
>  }
>  EXPORT_SYMBOL_GPL(__video_device_state_free);
>  
> +struct v4l2_format *video_device_state_get_fmt(struct video_device_state *state)
> +{
> +	if (WARN_ON_ONCE(!state))
> +		return NULL;
> +
> +	return &state->fmt;
> +}
> +EXPORT_SYMBOL_GPL(video_device_state_get_fmt);
> +
> +int video_device_g_fmt(struct file *file, void *priv, struct v4l2_format *fmt)
> +{
> +	struct video_device_state *state = priv;
> +	struct v4l2_format *vfmt = video_device_state_get_fmt(state);

Obviously, if multiple format types are stored in state (e.g. video capture and
output), then this code needs to pick the right format based on fmt->type.

I would also suggest moving this to v4l2-common.c and renaming it to v4l2_g_fmt,
consistent with other helpers there (v4l2_g/s_parm_cap).

Regards,

	Hans

> +
> +	if (!vfmt)
> +		return -EINVAL;
> +
> +	*fmt = *vfmt;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(video_device_g_fmt);
> +
>  static inline void video_get(struct video_device *vdev)
>  {
>  	get_device(&vdev->dev);
> diff --git a/include/media/v4l2-dev.h b/include/media/v4l2-dev.h
> index d327be16f6def70554a7d92d10436a29384ae32a..b5312823fbff9c236d4394d48fa9a14412b17c68 100644
> --- a/include/media/v4l2-dev.h
> +++ b/include/media/v4l2-dev.h
> @@ -612,6 +612,24 @@ __video_device_state_alloc(struct video_device *vdev,
>   */
>  void __video_device_state_free(struct video_device_state *state);
>  
> +/**
> + * video_device_state_get_fmt - get current v4l2_format.
> + *
> + * @state: pointer to struct video_device_state
> + */
> +struct v4l2_format *
> +video_device_state_get_fmt(struct video_device_state *state);
> +
> +/**
> + * video_device_g_fmt - fill v4l2_format from the state.
> + *
> + * @file: pointer to struct file
> + * @state: pointer to struct video_device_state
> + * @format: pointer to struct v4l2_format
> + */
> +int video_device_g_fmt(struct file *file, void *priv,
> +		       struct v4l2_format *format);
> +
>  /**
>   * v4l2_debugfs_root - returns the dentry of the top-level "v4l2" debugfs dir
>   *
>