From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 656096B002D for ; Wed, 12 Oct 2011 11:19:10 -0400 (EDT) Received: by bkbzs2 with SMTP id zs2so264907bkb.14 for ; Wed, 12 Oct 2011 08:19:06 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1318325033-32688-1-git-send-email-sumit.semwal@ti.com> <1318325033-32688-2-git-send-email-sumit.semwal@ti.com> Date: Wed, 12 Oct 2011 10:15:25 -0500 Message-ID: Subject: Re: [Linaro-mm-sig] [RFC 1/2] dma-buf: Introduce dma buffer sharing mechanism From: Rob Clark Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Dave Airlie Cc: Sumit Semwal , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linux@arm.linux.org.uk, arnd@arndb.de, jesse.barker@linaro.org, daniel@ffwll.ch On Wed, Oct 12, 2011 at 9:34 AM, Dave Airlie wrote: > On Wed, Oct 12, 2011 at 3:24 PM, Rob Clark wrote: >> On Wed, Oct 12, 2011 at 9:01 AM, Dave Airlie wrote: >>>> But then we'd need a different set of accessors for every different >>>> drm/v4l/etc driver, wouldn't we? >>> >>> Not any more different than you need for this, you just have a new >>> interface that you request a sw object from, >>> then mmap that object, and underneath it knows who owns it in the kerne= l. >> >> oh, ok, so you are talking about a kernel level interface, rather than >> userspace.. >> >> but I guess in this case I don't quite see the difference. =A0It amounts >> to which fd you call mmap (or ioctl[*]) on.. =A0If you use the dmabuf fd >> directly then you don't have to pass around a 2nd fd. >> >> [*] there is nothing stopping defining some dmabuf ioctls (such as for >> synchronization).. although the thinking was to keep it simple for >> first version of dmabuf >> > > Yes a separate kernel level interface. I'm not against it, but if it is a device-independent interface, it just seems like six of one, half-dozen of the other.. Ie. how does it differ if the dmabuf fd is the fd used for ioctl/mmap, vs if some other /dev/buffer-sharer file that you open? But I think maybe I'm misunderstanding what you have in mind? BR, -R > Well I'd like to keep it even simpler. dmabuf is a buffer sharing API, > shoehorning in a sw mapping API isn't making it simpler. > > The problem I have with implementing mmap on the sharing fd, is that > nothing says this should be purely optional and userspace shouldn't > rely on it. > > In the Intel GEM space alone you have two types of mapping, one direct > to shmem one via GTT, the GTT could be even be a linear view. The > intel guys initially did GEM mmaps direct to the shmem pages because > it seemed simple, up until they > had to do step two which was do mmaps on the GTT copy and ended up > having two separate mmap methods. I think the problem here is it seems > deceptively simple to add this to the API now because the API is > simple, however I think in the future it'll become a burden that we'll > have to workaround. > > Dave. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org