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

[Christoph Hellwig]

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.