Hi Jacopo
On Mon, 7 Nov 2022 at 20:50, Jacopo Mondi <jacopo@xxxxxxxxxx> wrote:
>
> The maximum achieable exposure time in a camera sensor is usually
s/achieable/achievable
> bound by the total frame height (visible + blankings) minus a fixed
> sensor-speific offset.
s/speific/specific
visible, or analogue crop?
> When the vertical blanking control value is changed, the exposure
> control limits should be updated as well.
>
> Add this to the camera sensor documentation.
>
> Signed-off-by: Jacopo Mondi <jacopo@xxxxxxxxxx>
> ---
> .../driver-api/media/camera-sensor.rst | 33 +++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst
> index 31f74f85ebc5..76206c7647d6 100644
> --- a/Documentation/driver-api/media/camera-sensor.rst
> +++ b/Documentation/driver-api/media/camera-sensor.rst
> @@ -179,3 +179,36 @@ used to obtain device's power state after the power state transition:
> The function returns a non-zero value if it succeeded getting the power count or
> runtime PM was disabled, in either of which cases the driver may proceed to
> access the device.
> +
> +Resetting exposure on vertical blanking update
Resetting exposure limits on vertical blanking update
You don't want to update the value (unless it is now outside the
permissible range).
> +""""""""""""""""""""""""""""""""""""""""""""""
> +
> +The sensor exposure time, specified by the ``V4L2_CID_EXPOSURE`` control, is
> +usually limited by a maximum value which is equal to maximum vertical blankings
> +minus a known offset usually specified in the chip programming manual.
limited to a maximum value related to the frame interval. Frequently
it is a number of lines less than the frame length that will be
specified in the sensor documentation.
> +When a new ``V4L2_CID_VBLANK`` value is applied, regardless of it being actually
> +programmed to the hardware or not, the limits of the ``V4L2_CID_EXPOSURE``
> +control should be updated as well.
> +
> +The typical coding pattern that realizes that in the ``.s_ctrl`` callback
> +handler is:
> +
> +.. code-block:: c
> +
#define SENSOR_EXPOSURE_OFFSET <see sensor documentation>
> + static int s_ctrl(struct v4l2_ctrl *ctrl)
> + {
> + int exp_max;
> +
> + switch (ctrl->id) {
> + case V4L2_CID_VBLANK:
> + exp_max = sensor->fmt.height + ctrl->val - 4;
sensor->fmt.height + ctrl->val - SENSOR_EXPOSURE_OFFSET.
Discussion on patch 1 over the use of sensor->fmt.height.
Dave
> + __v4l2_ctrl_modify_range(sensor->ctrls.exposure,
> + sensor->ctrls.exposure->minimum,
> + exp_max, sensor->ctrls.exposure->step,
> + sensor->ctrls.exposure->default_value);
> + break;
> + }
> +
> + if (!pm_runtime_get_if_in_use(&sensor->i2c_client->dev))
> + return 0;
> --
> 2.38.1
>
