Re: Regression: 6eb0233ec2d0 ("usb: don't inherity DMA properties for USB devices")

On Thu, Feb 18, 2021 at 04:21:26PM +0100, Thomas Zimmermann wrote:

Sure, it's at [1]. For udl, the dmabuf would need to be in system memory. 
The driver creates urbs from the framebuffer content and sends them to the 
device for displaying.

My question is more: what's the best interface to do this? Is there example 
code somewhere?

URBs do point to system memory most of the time.  I'm not a real USB
expert, but usb-storage or uas would be classic examples for drivers
that take arbitrary memory controller by another layer and do DMA to/from
that.