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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 CB020CA9EB9 for ; Thu, 24 Oct 2019 01:11:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A190D20650 for ; Thu, 24 Oct 2019 01:11:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390009AbfJXBLC (ORCPT ); Wed, 23 Oct 2019 21:11:02 -0400 Received: from verein.lst.de ([213.95.11.211]:43036 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388218AbfJXBLC (ORCPT ); Wed, 23 Oct 2019 21:11:02 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id BD36968BE1; Thu, 24 Oct 2019 03:10:59 +0200 (CEST) Date: Thu, 24 Oct 2019 03:10:59 +0200 From: Christoph Hellwig To: Alan Stern Cc: Greg KH , Oliver Neukum , Piergiorgio Sartor , Seth Bollinger , Christoph Hellwig , Jens Axboe , USB list Subject: Re: [PATCH] UAS: Revert commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments") Message-ID: <20191024011059.GB5067@lst.de> References: <20191023015348.GA16123@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Wed, Oct 23, 2019 at 11:34:33AM -0400, Alan Stern wrote: > Commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments"), > copying a similar commit for usb-storage, attempted to solve a problem > involving scatter-gather I/O and USB/IP by setting the > virt_boundary_mask for mass-storage devices. > > However, it now turns out that the analogous change in usb-storage > interacted badly with commit 09324d32d2a0 ("block: force an unlimited > segment size on queues with a virt boundary"), which was added later. > A typical error message is: > > ehci-pci 0000:00:13.2: swiotlb buffer is full (sz: 327680 bytes), > total 32768 (slots), used 97 (slots) > > There is no longer any reason to keep the virt_boundary_mask setting > in the uas driver. It was needed in the first place only for > handling devices with a block size smaller than the maxpacket size and > where the host controller was not capable of fully general > scatter-gather operation (that is, able to merge two SG segments into > a single USB packet). But: > > High-speed or slower connections never use a bulk maxpacket > value larger than 512; > > The SCSI layer does not handle block devices with a block size > smaller than 512 bytes; > > All the host controllers capable of SuperSpeed operation can > handle fully general SG; > > Since commit ea44d190764b ("usbip: Implement SG support to > vhci-hcd and stub driver") was merged, the USB/IP driver can > also handle SG. > > Therefore all supported device/controller combinations should be okay > with no need for any special virt_boundary_mask. So in order to head > off potential problems similar to those affecting usb-storage, this > patch reverts commit 3ae62a42090f. > > Signed-off-by: Alan Stern > CC: Oliver Neukum > CC: Looks good, Acked-by: Christoph Hellwig