From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from perceval.ideasonboard.com ([95.142.166.194]:54283 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754439Ab2GaVw2 convert rfc822-to-8bit (ORCPT ); Tue, 31 Jul 2012 17:52:28 -0400 From: Laurent Pinchart To: =?ISO-8859-1?Q?R=E9mi?= Denis-Courmont 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 Subject: Re: [PATCHv2 3/9] v4l: add buffer exporting via dmabuf Date: Tue, 31 Jul 2012 23:52:35 +0200 Message-ID: <1376487.cHbjGZJEZg@avalon> In-Reply-To: <201207312139.42818.remi@remlab.net> References: <1339684349-28882-1-git-send-email-t.stanislaws@samsung.com> <26877422.izWOc7eKQo@avalon> <201207312139.42818.remi@remlab.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="iso-8859-1" Sender: linux-media-owner@vger.kernel.org List-ID: Hi Rémi, On Tuesday 31 July 2012 21:39:40 Rémi Denis-Courmont wrote: > Le mardi 31 juillet 2012 19:28:12 Laurent Pinchart, vous avez écrit : > > On Tuesday 31 July 2012 16:39:00 Rémi Denis-Courmont wrote: > > > Le mardi 31 juillet 2012 14:56:14 Laurent Pinchart, vous avez écrit : > > > > > For that matter, wouldn't it be useful to support exporting a > > > > > userptr > > > > > buffer at some point in the future? > > > > > > > > Shouldn't USERPTR usage be discouraged once we get dma-buf support ? > > > > > > USERPTR, where available, is currently the only way to perform zero-copy > > > from kernel to userspace. READWRITE does not support zero-copy at all. > > > MMAP only supports zero-copy if userspace knows a boundary on the number > > > of concurrent buffers *and* the device can deal with that number of > > > buffers; in general, MMAP requires memory copying. > > > > Could you please share your use case(s) with us ? > > I want to receive the video buffers in user space for processing. Typically > "processing" is software encoding or conversion. That's what virtually any > V4L application does on the desktop... But what prevents you from using MMAP ? -- Regards, Laurent Pinchart