Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f7/STM32F767/DSI/DSI_LPCR#0x0
DSI Host LTDC Polarity Configuration Register
Data Enable Polarity
VSYNC Polarity
HSYNC Polarity
https://github.com/modm-io/cmsis-svd-stm32