Howto create custom PHY driver for CubeMX? Need support for KSZ8081.

Hello since a while ST changed the way CubeMX interacts with PHY driver.

Is ist possible to write my own BSP package for CubeMX?

And how ? Is there any documentation.

I am using Microchip/Micrel KSZ8081 on MII STM32F437

Thanks and regards.

Adib.