Re: [PATCH v5 5/8] usb: mausb_host: Introduce PAL processing

[Alan Stern]

On Sun, 26 Apr 2020, Vladimir Stankovic wrote:

> On 26.4.20. 02:32, Alan Stern wrote:
> > On Sat, 25 Apr 2020 vladimir.stankovic@xxxxxxxxxxxxxxx wrote:
> > 
> >> Protocol adaptation layer (PAL) implementation has been added to
> >> introduce MA-USB structures and logic.
> >>
> >> Signed-off-by: Vladimir Stankovic <vladimir.stankovic@xxxxxxxxxxxxxxx>
> > 
> > ...
> > 
> >> +	/*
> >> +	 * 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