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Diffstat (limited to 'Documentation/driver-api/media/camera-sensor.rst')
| -rw-r--r-- | Documentation/driver-api/media/camera-sensor.rst | 45 |
1 files changed, 17 insertions, 28 deletions
diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst index 7160336aa475..c7d4891bd24e 100644 --- a/Documentation/driver-api/media/camera-sensor.rst +++ b/Documentation/driver-api/media/camera-sensor.rst @@ -3,10 +3,10 @@ Writing camera sensor drivers ============================= -CSI-2 ------ +CSI-2 and parallel (BT.601 and BT.656) busses +--------------------------------------------- -Please see what is written on :ref:`MIPI_CSI_2`. +Please see :ref:`transmitter-receiver`. Handling clocks --------------- @@ -26,15 +26,16 @@ user. ACPI ~~~~ -Read the "clock-frequency" _DSD property to denote the frequency. The driver can -rely on this frequency being used. +Read the ``clock-frequency`` _DSD property to denote the frequency. The driver +can rely on this frequency being used. Devicetree ~~~~~~~~~~ -The currently preferred way to achieve this is using "assigned-clock-rates" -property. See Documentation/devicetree/bindings/clock/clock-bindings.txt for -more information. The driver then gets the frequency using clk_get_rate(). +The currently preferred way to achieve this is using ``assigned-clocks``, +``assigned-clock-parents`` and ``assigned-clock-rates`` properties. See +``Documentation/devicetree/bindings/clock/clock-bindings.txt`` for more +information. The driver then gets the frequency using ``clk_get_rate()``. This approach has the drawback that there's no guarantee that the frequency hasn't been modified directly or indirectly by another driver, or supported by @@ -55,7 +56,7 @@ processing pipeline as one or more sub-devices with different cropping and scaling configurations. The output size of the device is the result of a series of cropping and scaling operations from the device's pixel array's size. -An example of such a driver is the smiapp driver (see drivers/media/i2c/smiapp). +An example of such a driver is the CCS driver (see ``drivers/media/i2c/ccs``). Register list based drivers ~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -67,7 +68,7 @@ level are independent. How a driver picks such configuration is based on the format set on a source pad at the end of the device's internal pipeline. Most sensor drivers are implemented this way, see e.g. -drivers/media/i2c/imx319.c for an example. +``drivers/media/i2c/imx319.c`` for an example. Frame interval configuration ---------------------------- @@ -94,9 +95,10 @@ large variety of devices beyond camera sensors. Devices that have no analogue crop, use the full source image size, i.e. pixel array size. Horizontal and vertical blanking are specified by ``V4L2_CID_HBLANK`` and -``V4L2_CID_VBLANK``, respectively. The unit of these controls are lines. The -pixel rate is specified by ``V4L2_CID_PIXEL_RATE`` in the same sub-device. The -unit of that control is Hz. +``V4L2_CID_VBLANK``, respectively. The unit of the ``V4L2_CID_HBLANK`` control +is pixels and the unit of the ``V4L2_CID_VBLANK`` is lines. The pixel rate in +the sensor's **pixel array** is specified by ``V4L2_CID_PIXEL_RATE`` in the same +sub-device. The unit of that control is pixels per second. Register list based drivers need to implement read-only sub-device nodes for the purpose. Devices that are not register list based need these to configure the @@ -125,14 +127,14 @@ general, the device must be powered on at least when its registers are being accessed and when it is streaming. Existing camera sensor drivers may rely on the old -:c:type:`v4l2_subdev_core_ops`->s_power() callback for bridge or ISP drivers to +struct v4l2_subdev_core_ops->s_power() callback for bridge or ISP drivers to manage their power state. This is however **deprecated**. If you feel you need to begin calling an s_power from an ISP or a bridge driver, instead please add runtime PM support to the sensor driver you are using. Likewise, new drivers should not use s_power. Please see examples in e.g. ``drivers/media/i2c/ov8856.c`` and -``drivers/media/i2c/smiapp/smiapp-core.c``. The two drivers work in both ACPI +``drivers/media/i2c/ccs/ccs-core.c``. The two drivers work in both ACPI and DT based systems. Control framework @@ -149,16 +151,3 @@ 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. - -Controls --------- - -For camera sensors that are connected to a bus where transmitter and receiver -require common configuration set by drivers, such as CSI-2 or parallel (BT.601 -or BT.656) bus, the ``V4L2_CID_LINK_FREQ`` control is mandatory on transmitter -drivers. Receiver drivers can use the ``V4L2_CID_LINK_FREQ`` to query the -frequency used on the bus. - -The transmitter drivers should also implement ``V4L2_CID_PIXEL_RATE`` control in -order to tell the maximum pixel rate to the receiver. This is required on raw -camera sensors. |