From mboxrd@z Thu Jan 1 00:00:00 1970 From: "=?iso-8859-1?q?R=E9mi?= Denis-Courmont" Subject: Re: [PATCHv2 3/9] v4l: add buffer exporting via dmabuf Date: Tue, 31 Jul 2012 16:39:00 +0300 Message-ID: <201207311639.02693.remi@remlab.net> References: <1339684349-28882-1-git-send-email-t.stanislaws@samsung.com> <201207310833.56566.hverkuil@xs4all.nl> <36319543.mdnBULUSen@avalon> Mime-Version: 1.0 Content-Type: Text/Plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <36319543.mdnBULUSen@avalon> Sender: linux-media-owner@vger.kernel.org To: Laurent Pinchart Cc: Hans Verkuil , Tomasz Stanislawski , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, airlied@redhat.com, m.szyprowski@samsung.com, kyungmin.park@samsung.com, sumit.semwal@ti.com, daeinki@gmail.com, daniel.vetter@ffwll.ch, robdclark@gmail.com, pawel@osciak.com, linaro-mm-sig@lists.linaro.org, subashrp@gmail.com, mchehab@redhat.com, g.liakhovetski@gmx.de List-Id: dri-devel@lists.freedesktop.org Le mardi 31 juillet 2012 14:56:14 Laurent Pinchart, vous avez =E9crit : > > For that matter, wouldn't it be useful to support exporting a userp= tr > > buffer at some point in the future? >=20 > Shouldn't USERPTR usage be discouraged once we get dma-buf support ? USERPTR, where available, is currently the only way to perform zero-cop= y from=20 kernel to userspace. READWRITE does not support zero-copy at all. MMAP = only=20 supports zero-copy if userspace knows a boundary on the number of concu= rrent=20 buffers *and* the device can deal with that number of buffers; in gener= al,=20 MMAP requires memory copying. I am not sure DMABUF even supports transmitting data efficiently to use= rspace.=20 In my understanding, it's meant for transmitting data between DSP's byp= assing=20 userspace entirely, in other words the exact opposite of what USERBUF d= oes. --=20 R=E9mi Denis-Courmont http://www.remlab.net/ http://fi.linkedin.com/in/remidenis