Have been troubleshooting what I thought was a hardware issue on my custom Carambola2 board which uses GPIO11 as one of the SPI CS lines.

As usual the solution is simple - GPIO11 is by default fixed as an input for Jumpstart.

To use it as an output you need to run "mmio -b 0x18040030 0x00070200" first - that will disable jumpstart and allow GPIO11 for other uses e.g. SPI.

Hopefully this will save someone else some time fooling around, googling unsuccessfully etc.!