From owner-freebsd-usb@FreeBSD.ORG Tue Dec 23 09:31:10 2014 Return-Path: Delivered-To: freebsd-usb@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id C0311886; Tue, 23 Dec 2014 09:31:10 +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 7E1361BB6; Tue, 23 Dec 2014 09:31:10 +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 D0D7A1FE022; Tue, 23 Dec 2014 10:31:07 +0100 (CET) Message-ID: <54993683.7010901@selasky.org> Date: Tue, 23 Dec 2014 10:31:47 +0100 From: Hans Petter Selasky User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Ian Lepore Subject: Re: About XHCI_TD_PAGE_SIZE. References: <549541BC.6070505@selasky.org> <20141222.103833.2105768702793613386.okuno.kohji@jp.panasonic.com> <5497E016.7020809@selasky.org> <20141222.183157.253796126986510571.okuno.kohji@jp.panasonic.com> <5497E8F2.5080800@selasky.org> <1419259745.1018.113.camel@freebsd.org> In-Reply-To: <1419259745.1018.113.camel@freebsd.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-usb@freebsd.org X-BeenThere: freebsd-usb@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: FreeBSD support for USB List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 23 Dec 2014 09:31:10 -0000 On 12/22/14 15:49, Ian Lepore wrote: > On Mon, 2014-12-22 at 10:48 +0100, Hans Petter Selasky wrote: >> On 12/22/14 10:31, Kohji Okuno wrote: >>> In an optimisation, we should reduce the number of LINK_TRB, too. >>> I heard from a LSI engineer that, >>> Generally xhci controler has the cache of TRB array. But, LINK_TRB >>> may make the cache miss. >> >> Hi, >> >> One reason for the additional link TRB's is that I think there is >> different behaviour among the XHCI implementations how and when they >> generate a completion event. Any changes we make in that area needs to >> be tested with different XHCI controllers. >> >> Currently only the umass driver will use transfers greater than 64KBytes >> in case of USB 3.0. Else the most common case is transfers below >> 64KBytes, except for custom apps. >> >> I have another idea pending, which is related to performance, but not >> the XHCI. I was thinking that the FreeBSD libusb could be extended to >> allocate a data buffer in the kernel which then gets mmapped to >> userspace, to save copying/copyout of USB transfer data. The problem >> about mmap() is that the buffers cannot be freed afterwards, and must >> remain in the kernel. >> >> What do you think? > > So you're going to be doing DMA directly in and out of buffers mapped > into userspace? I think that will fail on ARM and MIPS at least, and > maybe others (any platform that does cache maintenance based on virtual > addresses will be unable to do the maintenance reliably if the DMA > memory is mapped to multiple virtual addresses). The solution for that > is bounce buffers, which just gets you right back into copying the data. > > -- Ian > > > Right, so there is no way to make coherent memory mappings into userspace? --HPS