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Diffstat (limited to 'Documentation/driver-api/media/camera-sensor.rst')
| -rw-r--r-- | Documentation/driver-api/media/camera-sensor.rst | 33 |
1 files changed, 32 insertions, 1 deletions
diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst index 4d1ae12b9b4d..3fc378b3b269 100644 --- a/Documentation/driver-api/media/camera-sensor.rst +++ b/Documentation/driver-api/media/camera-sensor.rst @@ -15,7 +15,7 @@ Camera sensors have an internal clock tree including a PLL and a number of divisors. The clock tree is generally configured by the driver based on a few input parameters that are specific to the hardware:: the external clock frequency and the link frequency. The two parameters generally are obtained from system -firmware. No other frequencies should be used in any circumstances. +firmware. **No other frequencies should be used in any circumstances.** The reason why the clock frequencies are so important is that the clock signals come out of the SoC, and in many cases a specific frequency is designed to be @@ -23,6 +23,24 @@ used in the system. Using another frequency may cause harmful effects elsewhere. Therefore only the pre-determined frequencies are configurable by the user. +ACPI +~~~~ + +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(). + +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 +the board's clock tree to begin with. Changes to the Common Clock Framework API +are required to ensure reliability. + Frame size ---------- @@ -132,3 +150,16 @@ 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. |