Re: Video4Linux: Call an I2C subdev function to start a stream after a CSI2 driver has been started

[Terry Barnaby <terry1@beam.ltd.uk>]

Hi Kiera,

Thanks for you response. Yes its from the NXP Yocto distribution with 
kernel at: git://source.codeaurora.org/external/imx/linux-imx.git

But I wasn't after specific information/help with this platform, I was 
really trying to find out if there is a mechanism within the 
mainline/standard Video4Linux kernel API's such that a video front end 
subdev can get some function called once the video pipeline has been 
setup ie. All hardware modules configured and ready to run a video stream.

For example there is the s_stream() function pointer in 
v4l2_subdev_video_ops, but that function is called before the later (in 
pipeline) CSI2 module is started and I need a function to be called 
after all of the pipelines hardware has been initialised to get around 
this hardware feature/issue.

Terry
On 10/05/2022 16:33, Kieran Bingham wrote:
> Hi Terry,
>
> Quoting Terry Barnaby (2022-05-10 14:35:38)
>> Hi,
>>
>> We are working on a system that uses a NXP IMX8MP SOC with a TP2855
>> analogue video front end chip that can capture 1920x1080p25 or PAL
>> 720x576i25 analogue video streams which is generally working using
>> gstreamer as the higher level software driving this.
>>
>> We have an intermittent video stream start up problem which we believe
>> is down to:
>>
>> 1. The TP2855 is initialised first and its subdev *_s_stream() call is
>> called to start the video input.
>>
>> 2. The NXP CSI2 video input hardware is then started:
>> imx8-mipi-csi2-sam.c: mipi_csis_s_stream().
> I don't think I can see this file in the latest linux sources. Are you
> working on an out of tree BSP driver supported by a vendor?
>
> If so - you might be able to contact them directly for support, but if
> we don't have the source code it can be hard to support your issue.
>
> --
> Regards
>
> Kieran
>
>
>> 3. The TP2855 enables the CSI2 clock after its *_s_stream() call,
>> probably in hardware after its PLL's have locked, by sending a CSI2
>> start sequence on the CSI2 clock pair. This clock is then a continuous
>> clock ie. it does not go into low power mode during horizontal/vertical
>> blanking.
>>
>> 4. The NXP CSI2 video input hardware, based on some Samsung IP, does not
>> see the CSI2 clock unless it sees the CSI2 start sequence and depending
>> on timings it may not see this at video pipeline startup and we get not
>> video stream from the CSI2 hardware.
>>
>> I was hoping the subdev *_s_stream() call would be after all of the
>> hardware's pipeline was setup so I could instigate a CSI2 clock restart
>> in the TP2855 driver, but unfortunately this is called before the CSI2
>> hardware is setup.
>>
>> I can add a one shot timer to do this in the TP2855 subdev *_s_stream()
>> call, but obviously this is not ideal. Is there anyway to get a subdev
>> function called in the video4linux API automatically once all of the
>> video streams hardware is setup ?
>>
>> Any ideas/recommendations ?
>>
>> Terry
>>
>>