What's the purpose of the 1x2 header on m.2 SSDs?

On some m.2 SSDs, there is an unpopulated spot for a header at the screw end of the drive (as opposed to the edge connector end of the drive). What is the purpose and the pinout for this header?

See the pair of holes near where the screw is when installed, one of which has a square pcb pad around the hole, and the other a circular pad. That is what I refer to.

Solution 1:

The headers are actually an SPI or an I2C interface I believe, for debugging. It is sometimes written DO and DI (Digital In, Out perhaps?) :

This is the same labelling as in SD cards for SPI communication: Example

Many SSD have more open pins for debugging, such as this one which is clearly labelled:

You can see this one has an option for writing to the ROM of the SSD as well as JTAG options.

People have checked an successfully communicated with these headers:

https://www.pentestpartners.com/security-blog/walkthrough-investigating-an-ssd/