Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/SiFive/FU540/PRCI/gemgxlpllcfg1#0x0
Gigabit Ethernet PLL Configuration Register
PLL clock output enable. Glitch free clock gate after PLL output. 1 enables clock, 0 disables clock
https://github.com/cmsis-svd/cmsis-svd-data