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From: Jacopo Mondi <>
To: Sakari Ailus <>,
	Laurent Pinchart <>,
	Dave Stevenson <>,
	Hans Verkuil <>,
	Mauro Carvalho Chehab <>
Cc: Jacopo Mondi <>,
	Linux Media Mailing List <>
Subject: [PATCH v2 2/2] documentation: media: camera_sensor: Update exposure on blanking change
Date: Mon, 21 Nov 2022 19:15:15 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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 <>
 .../driver-api/media/camera-sensor.rst        | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst
index 382ea4ecebd4..675f55ad54b5 100644
--- a/Documentation/driver-api/media/camera-sensor.rst
+++ b/Documentation/driver-api/media/camera-sensor.rst
@@ -184,3 +184,39 @@ 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 limits on vertical blanking update
+The sensor exposure time, specified by the ``V4L2_CID_EXPOSURE`` control, is
+usually 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 = (analogue crop height) + ctrl->val - SENSOR_EXPOSURE_OFFSET;
+			__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;

      parent reply	other threads:[~2022-11-21 18:15 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-21 18:15 [PATCH v2 0/2] Documentation: media: camera_sensor: Document blankings handling Jacopo Mondi
2022-11-21 18:15 ` [PATCH v2 1/2] documentation: " Jacopo Mondi
2022-11-21 18:15 ` Jacopo Mondi [this message]

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