How this happens.. as I stated in my opening post, the normal i2c port on my pi is fried. No idea why, no 5v has been applied to it, but I must have done something wrong somewhere, as the SCL port is always low (0v). It might be that just the pullup is blown, or something else, fact is it's always low, even if I use it as GPIO output and set it to high. SDA does still work normally, when I configure that pin as normal GPIO, i can switch it between high/low.
Since I'm working on an embedded project which requires i2c, I was looking for a way to accomplish that, even thouhgh the i2c port was broken. The first thing I investigated, was to use the i2c ports I know are available on the camera and display ports, however, google didn't yield me results soon enough for that, so I took another look at the pinout. After some searching, I found the second i2c port on the 40 pin port. Then I googled on how to activate it. Found a lot of wrong answers, untill I finally found the answer I posted about here. So I googled a lot on camera and i2c and googled a lot on second i2c bus and stuff like that, and NOWHERE did I find that the camera uses that port. I wat totally ignorant to that, untill you posted it here.
So I can't really tell you exactly where to document it. All I can say, from a user perspective, that if you're googling to enable the 2nd I2C port, all you will find is the EEPROM story. Mostly because of this:
https://github.com/raspberrypi/hats/blo ... gnguide.md
Within the set of pins available on the J8 GPIO header, ID_SC and ID_SD (GPIO0/SCL and GPIO1/SDA) are reserved for board detection / identification. The only allowed connections to the ID_ pins are an ID EEPROM plus 3.9K pull up resistors. Do not connect anything else to these pins!
Which led me to believe that it's only used for an EEPROM. The other stuff (GPU) is not mentioned there.
I understand where you are coming from. You know the documents and know it's in there multiple times. All I'm saying is that if someone who's not intimately familiair with all the documents, and who's just googling for an answer, won't find this information.