From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932465Ab2AJBem (ORCPT ); Mon, 9 Jan 2012 20:34:42 -0500 Received: from mail-we0-f174.google.com ([74.125.82.174]:42628 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755930Ab2AJBek convert rfc822-to-8bit (ORCPT ); Mon, 9 Jan 2012 20:34:40 -0500 MIME-Version: 1.0 In-Reply-To: References: <1322816252-19955-1-git-send-email-sumit.semwal@ti.com> <1322816252-19955-2-git-send-email-sumit.semwal@ti.com> <20120109081030.GA3723@phenom.ffwll.local> Date: Tue, 10 Jan 2012 10:34:39 +0900 Message-ID: Subject: Re: [RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism From: InKi Dae To: Rob Clark 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, m.szyprowski@samsung.com, t.stanislaws@samsung.com, Sumit Semwal , daniel@ffwll.ch Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2012/1/10 Rob Clark : > On Mon, Jan 9, 2012 at 4:10 AM, InKi Dae wrote: >> note : in case of sharing a buffer between v4l2 and drm driver, the >> memory info would be copied vb2_xx_buf to xx_gem or xx_gem to >> vb2_xx_buf through sg table. in this case, only memory info is used to >> share, not some objects. > > which v4l2/vb2 patches are you looking at?  The patches I was using, > vb2 holds a reference to the 'struct dma_buf *' internally, not just > keeping the sg_table > yes, not keeping the sg_table. I mean... see a example below please. static void vb2_dma_contig_map_dmabuf(void *mem_priv) { struct sg_table *sg; ... sg = dma_buf_map_attachment(buf->db_attach, dir); ... buf->dma_addr = sg_dma_address(sg->sgl); ... } at least with no IOMMU, the memory information(containing physical memory address) would be copied to vb2_xx_buf object if drm gem exported its own buffer and vb2 wants to use that buffer at this time, sg table is used to share that buffer. and the problem I pointed out is that this buffer(also physical memory region) could be released by vb2 framework(as you know, vb2_xx_buf object and the memory region for buf->dma_addr pointing) but the Exporter(drm gem) couldn't know that so some problems would be induced once drm gem tries to release or access that buffer. and I have tried to resolve this issue adding get_shared_cnt() callback to dma-buf.h but I'm not sure that this is good way. maybe there would be better way. Thanks. > BR, > -R