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SubjectRe: [PATCH v4 04/21] doc: media/v4l-drivers: Add Qualcomm Camera Subsystem driver document
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Hi Hans,

On 18.08.2017 10:45, Hans Verkuil wrote:
> Hi Todor,
>
> A few small comments below:
>
> On 08/08/2017 03:30 PM, Todor Tomov wrote:
>> Add a document to describe Qualcomm Camera Subsystem driver.
>>
>> Signed-off-by: Todor Tomov <todor.tomov@linaro.org>
>> ---
>> 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.
>
> Can you explain what PIX and RDI stand for?
>
> I would also think it is a good idea to add a comment at the top of the various
> subdev sources that say a bit more than just "CSID Module".
>
> A simple "CSID (CSI Decoder) Module" is enough. Just so the reader knows what
> it is all about.
>
> Otherwise I don't have any more comments about this series.
>
> I don't need a v5 for this, if you can just post one patch for this documentation
> and one patch improving the source comments as described above, then that's
> fine with me.

Thank you for the review again.
I'll post two additional patches to add explanations of the abbreviations.

>
> Regards,
>
> Hans
>
>> +
>> +
>> +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/
>>
>

--
Best regards,
Todor Tomov

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