From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jakob Bornecrantz Subject: Re: dma-buf non-coherent mmap Date: Fri, 1 Nov 2013 01:17:44 +0100 Message-ID: References: <52728CA5.4030506@vmware.com> <5272C055.5010400@vmware.com> <5272C68D.7000409@vmware.com> <20131031230051.GK4167@phenom.ffwll.local> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ie0-f171.google.com (mail-ie0-f171.google.com [209.85.223.171]) by gabe.freedesktop.org (Postfix) with ESMTP id D795FF0105 for ; Thu, 31 Oct 2013 17:17:45 -0700 (PDT) Received: by mail-ie0-f171.google.com with SMTP id tp5so6468560ieb.30 for ; Thu, 31 Oct 2013 17:17:45 -0700 (PDT) In-Reply-To: <20131031230051.GK4167@phenom.ffwll.local> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dri-devel-bounces@lists.freedesktop.org Errors-To: dri-devel-bounces@lists.freedesktop.org To: Daniel Vetter Cc: "linaro-mm-sig@lists.linaro.org" , Daniel Vetter , Thomas Hellstrom , "dri-devel@lists.freedesktop.org" List-Id: dri-devel@lists.freedesktop.org On Fri, Nov 1, 2013 at 12:00 AM, Daniel Vetter wrote: > On Thu, Oct 31, 2013 at 10:07:25PM +0100, Thomas Hellstrom wrote: >> On 10/31/2013 09:48 PM, Dave Airlie wrote: >> >On Fri, Nov 1, 2013 at 6:40 AM, Thomas Hellstrom wrote: >> >>Well, I'd be happy to avoid mmap, but then what does optional mean in this >> >>context? >> >>That all generic user-space apps *must* implement a workaround if mmap isn't >> >>implemented? >> >> >> >>It's unfortunate a bit like implicit synchronization mentioned in section 3) >> >>in Direct Userspace Access/mmap Support >> >>in the kernel dma-buf doc: It should be avoided, otherwise it might be >> >>relied upon by userspace and exporters >> >>not implementing it will suffer. >> >> >> >>In reality, people will start using mmap() and won't care to implement >> >>workarounds if it's not supported, and drivers like >> >>vmwgfx and non-coherent architectures will suffer. >> >> >> >>I haven't looked closely at how DRI3 or Wayland/weston use or will use >> >>dma-buf, but if they rely on mmap, we're sort >> >>of lost. MIR uses the following scheme: >> >DRI3 and wayland won't use dma-buf mmap directly, >> > >> >using dma-buf mmap directly is wrong for anything that shares objects >> >with itself. >> >> That sounds good to hear. Perhaps we should add that to the dma-buf docs. > > Userspace mmap was essentially added as a concession to the android ion > guys since they really, really wanted it. We've tried to tell them that > it's a horrible idea (see all the fun with coherency and syncing), but > they said that they have userspace for it already and so we let it be. > > Imo if you're not running Android userspace there's no need for this at > all. But now it turns out that gstreamer is using it and our life is hell. We should have made it not work for _any_ driver if CONFIG_ANDRIOD wasn't set. Cheers, Jakob.