Vi2: low latency mode

[tobias.klinke]

Hi,

I’m using a custom camera with triggered image acquisition at Jetson Nano.
By default, there is a delay of two frames due to the ring buffer in vi_channel.c.
The low latency mode (v4l2-ctl -c low_latency_mode=1) solves the delay.

Now I wonder why low latency mode is not the default.

Looking at vi2_fops.c I basically just see the following differences:

1. In default mode, there is only one kthread that handles capturing and releasing buffers to user space.
   In low latency mode, there are two kthreads: one for capturing frames and one for releasing buffers to user space.
2. In default mode, frames are placed into a ring buffer and released with a two frames delay.
   In low latency mode frames are released as soon as MW_ACK_DONE syncpt is reached (so when frame is written to memory as far as I understand).

These differences don’t seem problematic to me.

So do I miss anything important?
Are there any disadvantages when using low latency mode in comparison to the default mode?

Thanks.

[ShaneCCC]

This mode was implement later and didn’t verify the stability enough to change it as default.
You can change the default value if there’s no any problem for your sensors.