Add a document to describe Qualcomm Camera Subsystem driver. Signed-off-by: Todor Tomov <todor.tomov@xxxxxxxxxx> --- Documentation/media/v4l-drivers/qcom_camss.rst | 124 +++++++++++++++++++++++++ 1 file changed, 124 insertions(+) create mode 100644 Documentation/media/v4l-drivers/qcom_camss.rst diff --git a/Documentation/media/v4l-drivers/qcom_camss.rst b/Documentation/media/v4l-drivers/qcom_camss.rst new file mode 100644 index 0000000..4707ea7 --- /dev/null +++ b/Documentation/media/v4l-drivers/qcom_camss.rst @@ -0,0 +1,124 @@ +.. include:: <isonum.txt> + +Qualcomm Camera Subsystem driver +================================ + +Introduction +------------ + +This file documents the Qualcomm Camera Subsystem driver located under +drivers/media/platform/qcom/camss-8x16. + +The current version of the driver supports the Camera Subsystem found on +Qualcomm MSM8916 and APQ8016 processors. + +The driver implements V4L2, Media controller and V4L2 subdev interfaces. +Camera sensor using V4L2 subdev interface in the kernel is supported. + +The driver is implemented using as a reference the Qualcomm Camera Subsystem +driver for Android as found in Code Aurora [#f1]_. + + +Qualcomm Camera Subsystem hardware +---------------------------------- + +The Camera Subsystem hardware found on 8x16 processors and supported by the +driver consists of: + +- 2 CSIPHY modules. They handle the Physical layer of the CSI2 receivers. + A separate camera sensor can be connected to each of the CSIPHY module; +- 2 CSID (CSI Decoder) modules. They handle the Protocol and Application layer + of the CSI2 receivers. A CSID can decode data stream from any of the CSIPHY. + Each CSID also contains a TG (Test Generator) block which can generate + artificial input data for test purposes; +- ISPIF (ISP Interface) module. Handles the routing of the data streams from + the CSIDs to the inputs of the VFE; +- VFE (Video Front End) module. Contains a pipeline of image processing hardware + blocks. The VFE has different input interfaces. The PIX input interface feeds + the input data to the image processing pipeline. Three RDI input interfaces + bypass the image processing pipeline. The VFE also contains the AXI bus + interface which writes the output data to memory. + + +Supported functionality +----------------------- + +The current version of the driver supports: + +- input from camera sensor via CSIPHY; +- generation of test input data by the TG in CSID; +- raw dump of the input data to memory. RDI interface of VFE is supported. + PIX interface (ISP processing, statistics engines, resize/crop, format + conversion) is not supported in the current version; +- concurrent and independent usage of two data inputs - could be camera sensors + and/or TG. + + +Driver Architecture and Design +------------------------------ + +The driver implements the V4L2 subdev interface. With the goal to model the +hardware links between the modules and to expose a clean, logical and usable +interface, the driver is split into V4L2 sub-devices as follows: + +- 2 CSIPHY sub-devices - each CSIPHY is represented by a single sub-device; +- 2 CSID sub-devices - each CSID is represented by a single sub-device; +- 2 ISPIF sub-devices - ISPIF is represented by a number of sub-devices equal + to the number of CSID sub-devices; +- 3 VFE sub-devices - VFE is represented by a number of sub-devices equal to + the number of RDI input interfaces. + +The considerations to split the driver in this particular way are as follows: + +- representing CSIPHY and CSID modules by a separate sub-device for each module + allows to model the hardware links between these modules; +- representing VFE by a separate sub-devices for each RDI input interface allows + to use the three RDI interfaces concurently and independently as this is + supported by the hardware; +- representing ISPIF by a number of sub-devices equal to the number of CSID + sub-devices allows to create linear media controller pipelines when using two + cameras simultaneously. This avoids branches in the pipelines which otherwise + will require a) userspace and b) media framework (e.g. power on/off + operations) to make assumptions about the data flow from a sink pad to a + source pad on a single media entity. + +Each VFE sub-device is linked to a separate video device node. + +The complete list of the media entities (V4L2 sub-devices and video device +nodes) is as follows: + +- msm_csiphy0 +- msm_csiphy1 +- msm_csid0 +- msm_csid1 +- msm_ispif0 +- msm_ispif1 +- msm_vfe0_rdi0 +- msm_vfe0_video0 +- msm_vfe0_rdi1 +- msm_vfe0_video1 +- msm_vfe0_rdi2 +- msm_vfe0_video2 + + +Implementation +-------------- + +Runtime configuration of the hardware (updating settings while streaming) is +not required to implement the currently supported functionality. The complete +configuration on each hardware module is applied on STREAMON ioctl based on +the current active media links, formats and controls set. + + +Documentation +------------- + +APQ8016 Specification: +https://developer.qualcomm.com/download/sd410/snapdragon-410-processor-device-specification.pdf +Referenced 2016-11-24. + + +References +---------- + +.. [#f1] https://source.codeaurora.org/quic/la/kernel/msm-3.10/ -- 2.7.4
