MIPI bus lane speed for IMX250/Xavier NX

[taldhous-imetrum]

We are using a pair of IMX250 cameras on a custom carrier (a minor variation of the devkit board) with a Xavier NX processor, configured to use four lanes per camera.

Based on a time of about 10ms for the difference between the start of frame and end of frame timestamps, it looks like the MIPI bus is running at 1Gb/s* rather than 1.5Gb/s which is the value specified in the IMX250 datasheet.

The max lane speed specified in the tegra-camera-platform device tree node is <1500000>.

What could cause the lane speed to be reduced to 1Gb/s, and is there a way to increase it to the maximum speed of 1.5Gb/s?

* Calculation for transfer rate is

transfer_rate = (image_width * image_height * bits_per_pixel) / (number_of_lanes * transfer_time)

(2043 * 2048 * 8) / (4 * 0.001) = 9,961,472,000 ~= 10ms.