> BTW, for usb devices, it probably depends on the host controller if 64bit > dma is possible or not. I guess most xhci controllers will be able to do > it.
The 4GB limitation is a simple solution to a wide variety of problems. Please describe a situation where 4GB of dma memory is a limitation. > > That said, I'm not 100% convinced the fear of bounce buffers is justified. > > If > > a USB device requires bouncing, it's already pretty slow. What are we > > optimizing for again? > > True for spinning disks or usb storage sticks. But an SSD attached via USB > 3.x is not slow. The buffer cache is cabable of doing flipping at the right point. I still cannot identify a need for 64 bit dma. Why?
