Camera preview (v4l2 overlay) on IMX8QXP

[MR1]

Good day everyone

The idea I'm exploring is to have DMA based preview on camera capture (ov5640 on IMX8QXP board). I found interesting experiment with dual channel isi configuration [1]. I would like to achieve something similar but one channel would be used to generate gray scale low resolution images for further CPU processing (hence small size required) CSI0->vc0->MEM and second channel would be 'shorted' to Display Controller 0 (CSI0->vc1->DC0) and forwarded to LVDS output with more pleasant resolution. In order for this to work the 'camera preview' isi channel should abduct display output on steam start and release it on steam stop. First question which arises: is it even possible? I'm not entirely sure as this plan was formed based on certain implicit consequences of described isi configuration in [1] and I failed to conduct experiment which would validate it. My assumption is this will require serious changes to isi drivers but unfortunately I'm not aware of any document with ISI registers description (like used in imx8-isi-hw.c). Hence I would appreciate any insight with two questions:
1) Is DMA based camera preview (aka v4l2 overlay) possible with proper handling of mentioned isi configuration?
2) Where can I find isi registers documentation which would allow me to implement missing functionality?

[1] https://www.nxp.com/docs/en/application-note/AN13430.pdf

[Dhruvit]

Hi @MR1,

I hope you are doing well.

One can use a zero-copy pipeline to use DMA for better execution speed.

Please refer to Chapter 14. Zero-copy Pipelines in i.MX 8 GStreamer User Guide.'

One can refer to 15.4.1.8.1 ISI Memory Map register descriptions in RM for ISI related register documentation.

Thanks & Regards,
Dhruvit Vasavada