Re: How to resolve an issue in swiotlb environment?

Alan Stern
2019-06-13T17:16:35Z

On Thu, 13 Jun 2019, Christoph Hellwig wrote:

> On Wed, Jun 12, 2019 at 10:43:11AM -0400, Alan Stern wrote:
> > Would it be okay to rely on the assumption that USB block devices never
> > have block size < 512? (We could even add code to the driver to
> > enforce this, although refusing to handle such devices at all might be
> > worse than getting an occasional error.)
>
> sd.c only supports a few specific sector size, and none of them is
> < 512 bytes:
>
> if (sector_size != 512 &&
> sector_size != 1024 &&
> sector_size != 2048 &&
> sector_size != 4096) {
> ...
> sdkp->capacity = 0;

Great! So all we have to do is fix vhci-hcd. Then we can remove all
the virt_boundary_mask stuff from usb-storage and uas entirely.

(I'm assuming wireless USB isn't a genuine issue. As far as I know, it
is pretty much abandoned at this point.)

Valentina and Shua: Adding SG support to vhci-hcd shouldn't be too
hard. It ought to be possible even without changing the network
protocol.

Alan Stern