The maximum achieable exposure time in a camera sensor is usually
bound by the total frame height (visible + blankings) minus a fixed
sensor-speific offset.
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
+""""""""""""""""""""""""""""""""""""""""""""""
+
+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.
+
+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
+
+ 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;
+ __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
