From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx203.postini.com [74.125.245.203]) by kanga.kvack.org (Postfix) with SMTP id 5150B6B005C for ; Tue, 20 Dec 2011 10:41:29 -0500 (EST) From: Arnd Bergmann Subject: Re: [Linaro-mm-sig] [RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism Date: Tue, 20 Dec 2011 15:41:17 +0000 References: <1322816252-19955-1-git-send-email-sumit.semwal@ti.com> <201112121648.52126.arnd@arndb.de> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201112201541.17904.arnd@arndb.de> Sender: owner-linux-mm@kvack.org List-ID: To: "Semwal, Sumit" Cc: Daniel Vetter , Alan Cox , linux@arm.linux.org.uk, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org On Monday 19 December 2011, Semwal, Sumit wrote: > I didn't see a consensus on whether dma_buf should enforce some form > of serialization within the API - so atleast for v1 of dma-buf, I > propose to 'not' impose a restriction, and we can tackle it (add new > ops or enforce as design?) whenever we see the first need of it - will > that be ok? [I am bending towards the thought that it is a problem to > solve at a bigger platform than dma_buf.] The problem is generally understood for streaming mappings with a single device using it: if you have a long-running mapping, you have to use dma_sync_*. This obviously falls apart if you have multiple devices and no serialization between the accesses. If you don't want serialization, that implies that we cannot have use the dma_sync_* API on the buffer, which in turn implies that we cannot have streaming mappings. I think that's ok, but then you have to bring back the mmap API on the buffer if you want to allow any driver to provide an mmap function for a shared buffer. Arnd -- 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