Re: How to resolve an issue in swiotlb environment?

Christoph Hellwig
2019-06-12T12:09:03Z

On Wed, Jun 12, 2019 at 01:46:06PM +0200, Oliver Neukum wrote:
> > Thay is someething the virt_boundary prevents. But could still give
> > you something like:
> >
> > 1536 4096 4096 1024
> >
> > or
> > 1536 16384 8192 4096 16384 512
>
> That would kill the driver, if maxpacket were 1024.
>
> USB has really two kinds of requirements
>
> 1. What comes from the protocol
> 2. What comes from the HCD
>
> The protocol wants just multiples of maxpacket. XHCI can satisfy
> that in arbitrary scatter/gather. Other HCs cannot.

We have no real way to enforce that for the other HCs unfortunately.
I can't really think of any better way to handle their limitations
except for setting max_segments to 1 or bounce buffering.