Dirty page-tacking with TTM

Hi, Christian,

I'm looking at adding a utility for tracking dirty pages for TTM. It's usable for non-coherent drivers to emulate coherent memory, for example for fbdev or if vmwgfx were to emulate coherent mappings, like required by Vulkan or by user-space dma-buf mappings.

Basically one would need to hook up the vm_ops page_mkwrite() and pfn_mkwrite() into ttm_bo_vm.c. That can be done with small stubs in ttm_bo_vm.c which call new functions in the ttm_bo driver. Alternatively we could have the driver provide the TTM vm ops, with the current as the default. I figure the rest can be done with helpers that initially can be part of vmwgfx and moved to TTM should other drivers be interested.

Does this sound OK with you?

/Thomas