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SubjectRe: [PATCH v5 5/8] usb: mausb_host: Introduce PAL processing
On Sun, 26 Apr 2020, Vladimir Stankovic wrote:

> On 26.4.20. 02:32, Alan Stern wrote:
> > On Sat, 25 Apr 2020 vladimir.stankovic@displaylink.com wrote:
> >
> >> Protocol adaptation layer (PAL) implementation has been added to
> >> introduce MA-USB structures and logic.
> >>
> >> Signed-off-by: Vladimir Stankovic <vladimir.stankovic@displaylink.com>
> >
> > ...
> >
> >> + /*
> >> + * Masking URB_SHORT_NOT_OK flag as SCSI driver is adding it where it
> >> + * should not, so it is breaking the USB drive on the linux
> >> + */
> >> + urb->transfer_flags &= ~URB_SHORT_NOT_OK;
> >
> > Removing the SHORT_NOT_OK flag is _not_ a valid thing to do. It will
> > cause drivers to malfunction.
> >
> > Can you please explain this comment?
> >
> > What SCSI driver?
> >
> > When is the flag being added?
> >
> > How does it break USB drives?
> >
> > Why haven't you already reported this problem to the
> > appropriate maintainers?
> >
> > Alan Stern
> >
>
> Hi,
>
> Issue that removal of SHORT_NOT_OK flag addressed is linked to particular
> set of Kingston USB 3.0 flash drives (super speed) - other USB flash drives
> haven't had this flag set. Without this "fix", those Kingston flash drives
> are not being enumerated properly.

Please explain in detail how the enumeration of these Kingston flash
drives fails. Or if such an explanation has already been posted,
please provide a link to it.

> This particular line was added in the early stage of development, during
> enumeration process implementation. The reason why it remained in the code
> since is because we haven't noticed any side-effects, even with various
> USB devices being attached to remote MA-USB device, including flash drives,
> cameras, wireless mice, etc.

Come to think of it, the SHORT_NOT_OK flag is mainly used with HCDs
that don't have scatter-gather support. Since your mausb driver does
support scatter-gather, you most likely won't encounter any problems
unless you go looking for them specifically.

> The problem has been reported, and is actively being investigated.

Where was the problem reported (URL to a mailing list archive)? Who is
investigating it?

> As soon as it gets addressed properly (w/o global negation of the flag),
> a new patch will be pushed.

Thank you.

Alan Stern

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