Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756100Ab0G0NsN (ORCPT ); Tue, 27 Jul 2010 09:48:13 -0400 Received: from mailout3.samsung.com ([203.254.224.33]:58936 "EHLO mailout3.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754289Ab0G0NsK (ORCPT ); Tue, 27 Jul 2010 09:48:10 -0400 Date: Tue, 27 Jul 2010 15:46:26 +0200 From: Marek Szyprowski Subject: RE: [PATCHv2 2/4] mm: cma: Contiguous Memory Allocator added In-reply-to: <20100727065842.40ae76c8@bike.lwn.net> To: "'Jonathan Corbet'" Cc: "'Russell King - ARM Linux'" , Michal Nazarewicz , linux-mm@kvack.org, "'Daniel Walker'" , Pawel Osciak , "'Mark Brown'" , linux-kernel@vger.kernel.org, "'Hiremath Vaibhav'" , "'FUJITA Tomonori'" , "'Kyungmin Park'" , "'Zach Pfeffer'" , linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org Message-id: <003f01cb2d92$20819730$6184c590$%szyprowski@samsung.com> MIME-version: 1.0 X-Mailer: Microsoft Office Outlook 12.0 Content-type: text/plain; charset=us-ascii Content-language: pl Content-transfer-encoding: 7BIT Thread-index: Acsti34hslJiPIn4THqABG1DyrvpiQABRawQ References: <743102607e2c5fb20e3c0676fadbcb93d501a78e.1280151963.git.m.nazarewicz@samsung.com> <20100727120841.GC11468@n2100.arm.linux.org.uk> <003701cb2d89$adae4580$090ad080$%szyprowski@samsung.com> <20100727065842.40ae76c8@bike.lwn.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1461 Lines: 38 Hello, On Tuesday, July 27, 2010 2:59 PM Jonathan Corbet wrote: > On Tue, 27 Jul 2010 14:45:58 +0200 > Marek Szyprowski wrote: > > > > How does one obtain the CPU address of this memory in order for the CPU > > > to access it? > > > > Right, we did not cover such case. In CMA approach we tried to separate > > memory allocation from the memory mapping into user/kernel space. Mapping > > a buffer is much more complicated process that cannot be handled in a > > generic way, so we decided to leave this for the device drivers. Usually > > video processing devices also don't need in-kernel mapping for such > > buffers at all. > > Still...that *is* why I suggested an interface which would return both > the DMA address and a kernel-space virtual address, just like the DMA > API does... Either that, or just return the void * kernel address and > let drivers do the DMA mapping themselves. Returning only the > dma_addr_t address will make the interface difficult to use in many > situations. As I said, drivers usually don't need in-kernel mapping for video buffers. Is there really a need for creating such mapping? Best regards -- Marek Szyprowski Samsung Poland R&D Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/