From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurent Pinchart Subject: Re: [PATCHv2 3/9] v4l: add buffer exporting via dmabuf Date: Thu, 02 Aug 2012 23:41:31 +0200 Message-ID: <191994915.iXxuxlMUSc@avalon> References: <1339684349-28882-1-git-send-email-t.stanislaws@samsung.com> <201208020835.58332.hverkuil@xs4all.nl> <201208020956.45291.remi@remlab.net> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <201208020956.45291.remi@remlab.net> Sender: linux-media-owner@vger.kernel.org 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 List-Id: dri-devel@lists.freedesktop.org Hi R=E9mi, On Thursday 02 August 2012 09:56:43 R=E9mi Denis-Courmont wrote: > Le jeudi 2 ao=FBt 2012 09:35:58 Hans Verkuil, vous avez =E9crit : > > On Wed August 1 2012 22:49:57 R=E9mi Denis-Courmont wrote: > > > > What about using the CREATE_BUFS ioctl to add new MMAP buffers = at > > > > runtime ? > > >=20 > > > Does CREATE_BUFS always work while already streaming has already > > > started? > > > If it depends on the driver, it's kinda helpless. > >=20 > > Yes, it does. It's one of the reasons it exists in the first place.= But > > there are currently only a handful of drivers that implement it. I = hope > > that as more and more drivers are converted to vb2 that the availab= ility > > of create_bufs will increase. >=20 > That's contradictory. If most drivers do not support it, then it won'= t work > during streaming. >=20 > > > What's the guaranteed minimum buffer count? It seems in any case,= MMAP > > > has a hard limit of 32 buffers (at least videobuf2 has), though o= ne > > > might argue this should be more than enough. > >=20 > > Minimum or maximum? The maximum is 32, that's hardcoded in the V4L2= core. > > Although drivers may force a lower maximum if they want. I have no = idea > > whether there are drivers that do that. There probably are. >=20 > The smallest of the maxima of all drivers. >=20 > > The minimum is usually between 1 and 3, depending on hardware limit= ations. >=20 > And that's clearly insufficient without memory copy to userspace buff= ers. That's the minimum number of buffers *required* by the hardware. You ca= n add=20 up to 32 buffers, I'm not aware of any driver that would prevent that. > It does not seem to me that CREATE_BUFS+MMAP is a useful replacement = for > REQBUFS+USERBUF then. --=20 Regards, Laurent Pinchart