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SPDX-License-Identifier: GPL-2.0 + +.. include:: <isonum.txt> + +Qualcomm Camera Subsystem driver +================================ + +Introduction +------------ + +This file documents the Qualcomm Camera Subsystem driver located under +drivers/media/platform/qcom/camss. + +The current version of the driver supports the Camera Subsystem found on +Qualcomm MSM8916/APQ8016 and MSM8996/APQ8096 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 Linaro [#f1]_ [#f2]_. + + +Qualcomm Camera Subsystem hardware +---------------------------------- + +The Camera Subsystem hardware found on 8x16 / 8x96 processors and supported by +the driver consists of: + +- 2 / 3 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 / 4 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; +- 1 / 2 VFE (Video Front End) module(s). Contain a pipeline of image processing + hardware blocks. The VFE has different input interfaces. The PIX (Pixel) input + interface feeds the input data to the image processing pipeline. The image + processing pipeline contains also a scale and crop module at the end. Three + RDI (Raw Dump Interface) 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; +- RDI interface of VFE + + - Raw dump of the input data to memory. + + Supported formats: + + - YUYV/UYVY/YVYU/VYUY (packed YUV 4:2:2 - V4L2_PIX_FMT_YUYV / + V4L2_PIX_FMT_UYVY / V4L2_PIX_FMT_YVYU / V4L2_PIX_FMT_VYUY); + - MIPI RAW8 (8bit Bayer RAW - V4L2_PIX_FMT_SRGGB8 / + V4L2_PIX_FMT_SGRBG8 / V4L2_PIX_FMT_SGBRG8 / V4L2_PIX_FMT_SBGGR8); + - MIPI RAW10 (10bit packed Bayer RAW - V4L2_PIX_FMT_SBGGR10P / + V4L2_PIX_FMT_SGBRG10P / V4L2_PIX_FMT_SGRBG10P / V4L2_PIX_FMT_SRGGB10P / + V4L2_PIX_FMT_Y10P); + - MIPI RAW12 (12bit packed Bayer RAW - V4L2_PIX_FMT_SRGGB12P / + V4L2_PIX_FMT_SGBRG12P / V4L2_PIX_FMT_SGRBG12P / V4L2_PIX_FMT_SRGGB12P). + - (8x96 only) MIPI RAW14 (14bit packed Bayer RAW - V4L2_PIX_FMT_SRGGB14P / + V4L2_PIX_FMT_SGBRG14P / V4L2_PIX_FMT_SGRBG14P / V4L2_PIX_FMT_SRGGB14P). + + - (8x96 only) Format conversion of the input data. + + Supported input formats: + + - MIPI RAW10 (10bit packed Bayer RAW - V4L2_PIX_FMT_SBGGR10P / V4L2_PIX_FMT_Y10P). + + Supported output formats: + + - Plain16 RAW10 (10bit unpacked Bayer RAW - V4L2_PIX_FMT_SBGGR10 / V4L2_PIX_FMT_Y10). + +- PIX interface of VFE + + - Format conversion of the input data. + + Supported input formats: + + - YUYV/UYVY/YVYU/VYUY (packed YUV 4:2:2 - V4L2_PIX_FMT_YUYV / + V4L2_PIX_FMT_UYVY / V4L2_PIX_FMT_YVYU / V4L2_PIX_FMT_VYUY). + + Supported output formats: + + - NV12/NV21 (two plane YUV 4:2:0 - V4L2_PIX_FMT_NV12 / V4L2_PIX_FMT_NV21); + - NV16/NV61 (two plane YUV 4:2:2 - V4L2_PIX_FMT_NV16 / V4L2_PIX_FMT_NV61). + - (8x96 only) YUYV/UYVY/YVYU/VYUY (packed YUV 4:2:2 - V4L2_PIX_FMT_YUYV / + V4L2_PIX_FMT_UYVY / V4L2_PIX_FMT_YVYU / V4L2_PIX_FMT_VYUY). + + - Scaling support. Configuration of the VFE Encoder Scale module + for downscalling with ratio up to 16x. + + - Cropping support. Configuration of the VFE Encoder Crop module. + +- Concurrent and independent usage of two (8x96: three) 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 (8x16 / 8x96): + +- 2 / 3 CSIPHY sub-devices - each CSIPHY is represented by a single sub-device; +- 2 / 4 CSID sub-devices - each CSID is represented by a single sub-device; +- 2 / 4 ISPIF sub-devices - ISPIF is represented by a number of sub-devices + equal to the number of CSID sub-devices; +- 4 / 8 VFE sub-devices - VFE is represented by a number of sub-devices equal to + the number of the input interfaces (3 RDI and 1 PIX for each VFE). + +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 input interface allows + to use the input interfaces concurrently 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 media controller pipeline graph is as follows (with connected two / three +OV5645 camera sensors): + +.. _qcom_camss_graph: + +.. kernel-figure:: qcom_camss_graph.dot + :alt: qcom_camss_graph.dot + :align: center + + Media pipeline graph 8x16 + +.. kernel-figure:: qcom_camss_8x96_graph.dot + :alt: qcom_camss_8x96_graph.dot + :align: center + + Media pipeline graph 8x96 + + +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. + +The output size of the scaler module in the VFE is configured with the actual +compose selection rectangle on the sink pad of the 'msm_vfe0_pix' entity. + +The crop output area of the crop module in the VFE is configured with the actual +crop selection rectangle on the source pad of the 'msm_vfe0_pix' entity. + + +Documentation +------------- + +APQ8016 Specification: +https://developer.qualcomm.com/download/sd410/snapdragon-410-processor-device-specification.pdf +Referenced 2016-11-24. + +APQ8096 Specification: +https://developer.qualcomm.com/download/sd820e/qualcomm-snapdragon-820e-processor-apq8096sge-device-specification.pdf +Referenced 2018-06-22. + +References +---------- + +.. [#f1] https://git.codelinaro.org/clo/la/kernel/msm-3.10/ +.. [#f2] https://git.codelinaro.org/clo/la/kernel/msm-3.18/ |