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: <175916260699.2234821.1165575981573312212@freya>
Date: Mon, 29 Sep 2025 21:46:46 +0530
From: Jai Luthra <jai.luthra@...asonboard.com>
To: Hans Verkuil <hverkuil+cisco@...nel.org>, Hans Verkuil <hverkuil@...nel.org>, Jacopo Mondi <jacopo.mondi@...asonboard.com>, Laurent Pinchart <laurent.pinchart@...asonboard.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, Sakari Ailus <sakari.ailus@...ux.intel.com>, Tomi Valkeinen <tomi.valkeinen@...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

Quoting Hans Verkuil (2025-09-22 13:36:59)
> 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).

Good catch, will fix in next revision.

> 
> Regards,
> 
>         Hans
> 
> > +
> > +     if (!vfmt)
> > +             return -EINVAL;
> > +
> > +     *fmt = *vfmt;
> > +
> > +     return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(video_device_g_fmt);
> > +

Thanks,
Jai

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