From owner-freebsd-current@FreeBSD.ORG Sat Apr 25 06:03:42 2015 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 62879502; Sat, 25 Apr 2015 06:03:42 +0000 (UTC) Received: from mail.turbocat.net (mail.turbocat.net [IPv6:2a01:4f8:d16:4514::2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 267881720; Sat, 25 Apr 2015 06:03:42 +0000 (UTC) Received: from laptop015.home.selasky.org (cm-176.74.213.204.customer.telag.net [176.74.213.204]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.turbocat.net (Postfix) with ESMTPSA id 357E41FE023; Sat, 25 Apr 2015 08:03:40 +0200 (CEST) Message-ID: <553B2E6B.20406@selasky.org> Date: Sat, 25 Apr 2015 08:04:27 +0200 From: Hans Petter Selasky User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Ian Lepore , Svatopluk Kraus CC: freebsd-current@freebsd.org Subject: Re: [patch] fix add_bounce_page() for BUS_DMA_KEEP_PG_OFFSET References: <1429882188.1157.2.camel@freebsd.org> <553B2D56.1000405@selasky.org> In-Reply-To: <553B2D56.1000405@selasky.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 25 Apr 2015 06:03:42 -0000 On 04/25/15 07:59, Hans Petter Selasky wrote: > On 04/24/15 15:29, Ian Lepore wrote: >> On Fri, 2015-04-24 at 13:34 +0200, Svatopluk Kraus wrote: >>> The add_bounce_page() can be called from _bus_dmamap_load_phys(). >>> Client virtual address is zero (not valid) in that case. So, client >>> physical address must be used to get an offset when >>> BUS_DMA_KEEP_PG_OFFSET flag is set. Note that client physical address >>> is always valid. >>> >>> Svatopluk Kraus >> >> The only user of BUS_DMA_KEEP_PG_OFFSET in the system is USB. If the >> flag didn't exist, we could do bouncing with a whole lot more >> efficiency, at least in the ARM world. I wonder if it would be possible >> to just eliminate the flag (and of course, USB's need for it, which I >> fully admit I don't understand even a little bit). >> > > Hi, > > USB (EHCI/UHCI/OHCI) needs this flag when computing scatter/gather > lists. Please ensure it works like expected. The good news is XHCI needs > it less than the EHCI. > > Ian: The patch looks good - will you commit it? > The reason is that the EHCI/UHCI/OHCI doesn't have separate length fields for each data chunk and somtimes use the "0x1000 - (addr & 0xFFF)" formula to compute how many bytes are left of a transfer when a transfer wraps around 0x1000. Thank you for you understanding this is not a USB problem in general. --HPS