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References: <20230609-v4l2-vtotal-v1-0-4b7dee7e073e@skidata.com> <20230609-v4l2-vtotal-v1-2-4b7dee7e073e@skidata.com>
In-Reply-To: <20230609-v4l2-vtotal-v1-2-4b7dee7e073e@skidata.com>
From:   Dave Stevenson <dave.stevenson@raspberrypi.com>
Date:   Fri, 9 Jun 2023 15:21:39 +0100
Message-ID: <CAPY8ntCx8QLX_jqtJeWzCQkApSR_+RY7jMM5pDNA7zewJa+eiA@mail.gmail.com>
Subject: Re: [PATCH 2/2] media: i2c: imx290: Add support for V4L2_CID_VTOTAL
To:     Benjamin Bara <bbara93@gmail.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Manivannan Sadhasivam <mani@kernel.org>,
        laurent.pinchart@ideasonboard.com, jacopo.mondi@ideasonboard.com,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        Benjamin Bara <benjamin.bara@skidata.com>
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Hi Benjamin

Thanks for the patch

On Fri, 9 Jun 2023 at 14:16, Benjamin Bara <bbara93@gmail.com> wrote:
>
> From: Benjamin Bara <benjamin.bara@skidata.com>
>
> The new V4L2_CID_VTOTAL control represents the VMAX register.
> Implementing it simplifies calculations in user space, as it is
> independent of the current mode (format height), meaning its value does
> not change with format changes.

I know Laurent suggested this change[1] so that (AIUI) exposure max
limits are easier to compute around mode changes.

I'm currently seeing this as a fair amount of boilerplate to be added
to all drivers so that two controls provide effectively the same
information, and I'm not convinced it saves any significant effort in
userspace. Can you (or Laurent) detail exactly what the issue is that
the new control solves?

Do we need to do the same for HBLANK as well, or do we live with an
asymmetrical set of controls.

Thanks
  Dave

[1] https://lists.libcamera.org/pipermail/libcamera-devel/2023-June/038170.html

> Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
> ---
>  drivers/media/i2c/imx290.c | 47 ++++++++++++++++++++++++++++++++++------------
>  1 file changed, 35 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/media/i2c/imx290.c b/drivers/media/i2c/imx290.c
> index 5ea25b7acc55..42938400efb0 100644
> --- a/drivers/media/i2c/imx290.c
> +++ b/drivers/media/i2c/imx290.c
> @@ -255,6 +255,7 @@ struct imx290 {
>         struct v4l2_ctrl *link_freq;
>         struct v4l2_ctrl *hblank;
>         struct v4l2_ctrl *vblank;
> +       struct v4l2_ctrl *vtotal;
>         struct v4l2_ctrl *exposure;
>         struct {
>                 struct v4l2_ctrl *hflip;
> @@ -782,8 +783,7 @@ static void imx290_exposure_update(struct imx290 *imx290,
>  {
>         unsigned int exposure_max;
>
> -       exposure_max = imx290->vblank->val + mode->height -
> -                      IMX290_EXPOSURE_OFFSET;
> +       exposure_max = imx290->vtotal->val - IMX290_EXPOSURE_OFFSET;
>         __v4l2_ctrl_modify_range(imx290->exposure, 1, exposure_max, 1,
>                                  exposure_max);
>  }
> @@ -794,7 +794,7 @@ static int imx290_set_ctrl(struct v4l2_ctrl *ctrl)
>                                              struct imx290, ctrls);
>         const struct v4l2_mbus_framefmt *format;
>         struct v4l2_subdev_state *state;
> -       int ret = 0, vmax;
> +       int ret = 0;
>
>         /*
>          * Return immediately for controls that don't need to be applied to the
> @@ -803,10 +803,22 @@ static int imx290_set_ctrl(struct v4l2_ctrl *ctrl)
>         if (ctrl->flags & V4L2_CTRL_FLAG_READ_ONLY)
>                 return 0;
>
> -       if (ctrl->id == V4L2_CID_VBLANK) {
> -               /* Changing vblank changes the allowed range for exposure. */
> +       /* Changing vtotal changes the allowed range for exposure. */
> +       if (ctrl->id == V4L2_CID_VTOTAL)
>                 imx290_exposure_update(imx290, imx290->current_mode);
> -       }
> +
> +       /*
> +        * vblank and vtotal depend on each other, therefore also update the
> +        * other one.
> +        */
> +       if (ctrl->id == V4L2_CID_VBLANK &&
> +           imx290->vtotal->val != ctrl->val + imx290->current_mode->height)
> +               __v4l2_ctrl_s_ctrl(imx290->vtotal,
> +                                  ctrl->val + imx290->current_mode->height);
> +       if (ctrl->id == V4L2_CID_VTOTAL &&
> +           imx290->vblank->val != ctrl->val - imx290->current_mode->height)
> +               __v4l2_ctrl_s_ctrl(imx290->vblank,
> +                                  ctrl->val - imx290->current_mode->height);
>
>         /* V4L2 controls values will be applied only when power is already up */
>         if (!pm_runtime_get_if_in_use(imx290->dev))
> @@ -821,9 +833,14 @@ static int imx290_set_ctrl(struct v4l2_ctrl *ctrl)
>                 break;
>
>         case V4L2_CID_VBLANK:
> -               ret = imx290_write(imx290, IMX290_VMAX,
> -                                  ctrl->val + imx290->current_mode->height,
> -                                  NULL);
> +               /* vblank is updated by vtotal. */
> +               break;
> +
> +       case V4L2_CID_VTOTAL:
> +               ret = imx290_write(imx290, IMX290_VMAX, ctrl->val, NULL);
> +               if (ret)
> +                       goto err;
> +
>                 /*
>                  * Due to the way that exposure is programmed in this sensor in
>                  * relation to VMAX, we have to reprogramme it whenever VMAX is
> @@ -834,9 +851,8 @@ static int imx290_set_ctrl(struct v4l2_ctrl *ctrl)
>                 ctrl = imx290->exposure;
>                 fallthrough;
>         case V4L2_CID_EXPOSURE:
> -               vmax = imx290->vblank->val + imx290->current_mode->height;
>                 ret = imx290_write(imx290, IMX290_SHS1,
> -                                  vmax - ctrl->val - 1, NULL);
> +                                  imx290->vtotal->val - ctrl->val - 1, NULL);
>                 break;
>
>         case V4L2_CID_TEST_PATTERN:
> @@ -880,6 +896,7 @@ static int imx290_set_ctrl(struct v4l2_ctrl *ctrl)
>                 break;
>         }
>
> +err:
>         pm_runtime_mark_last_busy(imx290->dev);
>         pm_runtime_put_autosuspend(imx290->dev);
>
> @@ -911,11 +928,14 @@ static void imx290_ctrl_update(struct imx290 *imx290,
>         unsigned int vblank_max = IMX290_VMAX_MAX - mode->height;
>
>         __v4l2_ctrl_s_ctrl(imx290->link_freq, mode->link_freq_index);
> +       __v4l2_ctrl_s_ctrl(imx290->vblank, imx290->vtotal->val - mode->height);
>
>         __v4l2_ctrl_modify_range(imx290->hblank, hblank_min, hblank_max, 1,
>                                  hblank_min);
>         __v4l2_ctrl_modify_range(imx290->vblank, vblank_min, vblank_max, 1,
>                                  vblank_min);
> +       __v4l2_ctrl_modify_range(imx290->vtotal, mode->vmax_min,
> +                                IMX290_VMAX_MAX, 1, mode->vmax_min);
>  }
>
>  static int imx290_ctrl_init(struct imx290 *imx290)
> @@ -947,7 +967,7 @@ static int imx290_ctrl_init(struct imx290 *imx290)
>
>         /*
>          * Correct range will be determined through imx290_ctrl_update setting
> -        * V4L2_CID_VBLANK.
> +        * V4L2_CID_VTOTAL.
>          */
>         imx290->exposure = v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops,
>                                              V4L2_CID_EXPOSURE, 1, 65535, 1,
> @@ -983,6 +1003,9 @@ static int imx290_ctrl_init(struct imx290 *imx290)
>
>         imx290->vblank = v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops,
>                                            V4L2_CID_VBLANK, 1, 1, 1, 1);
> +       imx290->vtotal = v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops,
> +                                          V4L2_CID_VTOTAL, 1, IMX290_VMAX_MAX,
> +                                          1, 1);
>
>         imx290->hflip = v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops,
>                                           V4L2_CID_HFLIP, 0, 1, 1, 0);
>
> --
> 2.34.1
>