From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71EABC54FCB for ; Sun, 26 Apr 2020 20:56:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 563DE2070A for ; Sun, 26 Apr 2020 20:56:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726360AbgDZU4n (ORCPT ); Sun, 26 Apr 2020 16:56:43 -0400 Received: from netrider.rowland.org ([192.131.102.5]:36453 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726177AbgDZU4n (ORCPT ); Sun, 26 Apr 2020 16:56:43 -0400 Received: (qmail 2181 invoked by uid 500); 26 Apr 2020 16:56:41 -0400 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 26 Apr 2020 16:56:41 -0400 Date: Sun, 26 Apr 2020 16:56:41 -0400 (EDT) From: Alan Stern X-X-Sender: stern@netrider.rowland.org To: Vladimir Stankovic cc: gregkh@linuxfoundation.org, , , Subject: Re: [External] Re: [PATCH v5 5/8] usb: mausb_host: Introduce PAL processing In-Reply-To: <871dcf46-19f8-f152-99c0-8185832ed109@displaylink.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 26 Apr 2020, Vladimir Stankovic wrote: > On 26.4.20. 16:31, Alan Stern wrote: > > 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 > >>> > >>> ... > >>> > >>>> + /* > >>>> + * 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. > > Will reproduce the issue once again (w/o the fix) and run through the events. > Issue has been noticed during early development, and addressed right away. > > > >> 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? > > Ticket has been submitted to DisplayLink's internal issue-tracking system > and is being investigated by mausb-host-devel team. Okay. What SCSI driver does the comment refer to? Is it something internal to DisplayLink or is it part of the regular Linux kernel? Alan Stern