linux-kernel - Re: [PATCH] media: v4l2-ctrl: Add p_def to v4l2_ctrl

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Date:   Wed, 16 Oct 2019 14:39:15 +0200
From:   Ricardo Ribalda Delgado <ribalda@...nel.org>
To:     Hans Verkuil <hverkuil-cisco@...all.nl>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: v4l2-ctrl: Add p_def to v4l2_ctrl_config

Hi Hans:

On Wed, Oct 16, 2019 at 2:32 PM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
>
> On 10/16/19 2:20 PM, Ricardo Ribalda Delgado wrote:
> > Hi Hans
> >
> > Not that awkward, the user has to use the brand new
> > v4l2_ctrl_ptr_create() ;). But if you prefer void * I can make the
> > change.
>
> Well, a struct v4l2_ctrl_config is typically a static const, so you can't use
> v4l2_ctrl_ptr_create().
>
> Hmm, perhaps it is as easy as:
>
> static const struct v4l2_area def_area = {
>         ...
> };
>
> static const struct v4l2_ctrl_config ctrl = {
>         ...
>
>         .p_def.p_area = &def_area,
>         ...
> };
>
> Can you do a quick compile check that I am not overlooking anything?
>
> If this works, then I'll take this patch.

Testing with gcc 9.2.1

This works fine, no warning/error:

static struct v4l2_area unit_size = {
.width = UNIT_SIZE,
.height = UNIT_SIZE,
};
static struct v4l2_ctrl_config area_ctrl = {
.type = V4L2_CTRL_TYPE_AREA,
.flags = V4L2_CTRL_FLAG_READ_ONLY,
.p_def.p_area = &unit_size,
};

but if unit_size is set as CONST:
static const struct v4l2_area

Then:
drivers/qtec/qtec_sony.c: In function ‘qtec_sony_probe’:
drivers/qtec/qtec_sony.c:3151:19: warning: initialization discards
‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
 3151 |   .p_def.p_area = &unit_size,
      |

>
> Regards,
>
>         Hans
>
> >
> > Regards
> >
> > On Wed, Oct 16, 2019 at 2:17 PM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
> >>
> >> On 10/14/19 4:14 PM, Ricardo Ribalda Delgado wrote:
> >>> This allows setting the default value on compound controls created via
> >>> v4l2_ctrl_new_custom.
> >>>
> >>> Signed-off-by: Ricardo Ribalda Delgado <ribalda@...nel.org>
> >>> ---
> >>>  drivers/media/v4l2-core/v4l2-ctrls.c | 2 +-
> >>>  include/media/v4l2-ctrls.h           | 2 ++
> >>>  2 files changed, 3 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> >>> index bf50d37ef6c1..12cf38f73f7b 100644
> >>> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> >>> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> >>> @@ -2583,7 +2583,7 @@ struct v4l2_ctrl *v4l2_ctrl_new_custom(struct v4l2_ctrl_handler *hdl,
> >>>                       type, min, max,
> >>>                       is_menu ? cfg->menu_skip_mask : step, def,
> >>>                       cfg->dims, cfg->elem_size,
> >>> -                     flags, qmenu, qmenu_int, ptr_null, priv);
> >>> +                     flags, qmenu, qmenu_int, cfg->p_def, priv);
> >>>       if (ctrl)
> >>>               ctrl->is_private = cfg->is_private;
> >>>       return ctrl;
> >>> diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
> >>> index 26205ba3a0a0..2fca5b823961 100644
> >>> --- a/include/media/v4l2-ctrls.h
> >>> +++ b/include/media/v4l2-ctrls.h
> >>> @@ -375,6 +375,7 @@ struct v4l2_ctrl_handler {
> >>>   * @max:     The control's maximum value.
> >>>   * @step:    The control's step value for non-menu controls.
> >>>   * @def:     The control's default value.
> >>> + * @p_def:   The control's default value for compound controls.
> >>>   * @dims:    The size of each dimension.
> >>>   * @elem_size:       The size in bytes of the control.
> >>>   * @flags:   The control's flags.
> >>> @@ -403,6 +404,7 @@ struct v4l2_ctrl_config {
> >>>       s64 max;
> >>>       u64 step;
> >>>       s64 def;
> >>> +     union v4l2_ctrl_ptr p_def;
> >>>       u32 dims[V4L2_CTRL_MAX_DIMS];
> >>>       u32 elem_size;
> >>>       u32 flags;
> >>>
> >>
> >> I'm not sure about this. It might be a bit awkward to initialize p_def given that it is a union.
> >>
> >> Perhaps a simple void pointer would be easier?
> >>
> >> Regards,
> >>
> >>         Hans
>