We have an application with a PCM5142 as I2S master. I finally managed to get it working using a forum post describing clocking for the PCM5122 and later found the data sheet for the PCM5242, which seems to describe the same things much better. I assume that the clocking works the same in PCM5122, PCM5142 and PCM5242? Are they perhaps fully register compatible? Anyway, there are still some gray areas in the PCM5242 data sheet.
What I would like to do, is to connect an external clock on a GPIO, use that as input to the PLL, output the PLLOUT/4 clock on some other GPIO and route that back (externally) to the SCK pin. That part works nicely. However, when the original external clock is already a good SCK, I would like the external clock to used directly as DAC reference, thus avoiding PLL gitter in the output whenever this is possible.
Looking at the clock diagram in the data sheet of both the PCM5142 and the PCM5242, this seems possible. In the diagram, the DAC Clock Source MUX has an input named GPIO. However, in the register description, SDAC (register 14, page 0) does not list GPIO as an option. Comparing to how SREF works (register 13, page 0) for the PLL, I also imagine that some other register is used to select which GPIO pin is actually used as DAC source. Or are the clocking trees simply wrong, and there is no possibility to use a GPIO pin as SDAC?