From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932855AbbHHKj5 (ORCPT ); Sat, 8 Aug 2015 06:39:57 -0400 Received: from mail-wi0-f171.google.com ([209.85.212.171]:38729 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932495AbbHHKjz convert rfc822-to-8bit (ORCPT ); Sat, 8 Aug 2015 06:39:55 -0400 From: Michal Nazarewicz To: Feng Tang Cc: Greg Kroah-Hartman , John Stultz , Andrew Morton , Kyungmin Park , Marek Szyprowski , Joonsoo Kim , LKML Subject: Re: [PATCH v2] staging: ion: Add a default struct device for cma heap In-Reply-To: <20150807155004.GA22612@shbuild888> Organization: http://mina86.com/ References: <1438919413-14440-1-git-send-email-feng.tang@intel.com> <20150807045404.GA26925@kroah.com> <20150807064601.GA9338@shbuild888> <20150807155004.GA22612@shbuild888> User-Agent: Notmuch/0.19+53~g2e63a09 (http://notmuchmail.org) Emacs/25.0.50.1 (x86_64-unknown-linux-gnu) X-Face: PbkBB1w#)bOqd`iCe"Ds{e+!C7`pkC9a|f)Qo^BMQvy\q5x3?vDQJeN(DS?|-^$uMti[3D*#^_Ts"pU$jBQLq~Ud6iNwAw_r_o_4]|JO?]}P_}Nc&"p#D(ZgUb4uCNPe7~a[DbPG0T~!&c.y$Ur,=N4RT>]dNpd;KFrfMCylc}gc??'U2j,!8%xdD Face: 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 X-PGP: 50751FF4 X-PGP-FP: AC1F 5F5C D418 88F8 CC84 5858 2060 4012 5075 1FF4 X-Hashcash: 1:20:150808:feng.tang@intel.com::eQK1++G3XtnKF5aQ:0000000000000000000000000000000000000000000E/6 X-Hashcash: 1:20:150808:akpm@linux-foundation.org::zul2jx/BhSxAETYm:0000000000000000000000000000000000001+lS X-Hashcash: 1:20:150808:m.szyprowski@samsung.com::y+Zt16zggKTC5oC5:00000000000000000000000000000000000003jbV X-Hashcash: 1:20:150808:kyungmin.park@samsung.com::OTemcCcoBbgnAI4H:0000000000000000000000000000000000005mLk X-Hashcash: 1:20:150808:gregkh@linuxfoundation.org::MCNneMhdBRbuS5DC:000000000000000000000000000000000006Sa4 X-Hashcash: 1:20:150808:iamjoonsoo.kim@lge.com::IVy+QmVAT88uynAq:0000000000000000000000000000000000000007y9m X-Hashcash: 1:20:150808:linux-kernel@vger.kernel.org::qIXKm20bz/pIV+0G:000000000000000000000000000000000650T X-Hashcash: 1:20:150808:john.stultz@linaro.org::0IINJ4KoIaD9mI2E:000000000000000000000000000000000000000C85T Date: Sat, 08 Aug 2015 12:39:48 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 07 2015, Feng Tang wrote: > For ion cma heap, the buffer allocation func ion_cma_allocate() will > call dma_alloc_coherent(dev, ...). And dma_alloc_coherent() is > implemented by each architeture(arm/m68k/x86 etc), and many Arch's > implementation doesn't use cma, but use alloc_pages() like APIs. So what you’re saying is that ‘ION CMA heap’ is a misnomer since it has to do with CMA only if given architecture implements dma_alloc_coherent using CMA. It should rather be called ‘ION DMA coherent heap’. This leads to realisation that the code should be oblivious to CMA areas and never operate on them directly (e.g. never accept struct cma * or use dev_set_cma_area). In the current form, if architecture does not use CMA, the whole dev_set_cma_area shenanigans are pointless. -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michał “mina86” Nazarewicz (o o) ooo +------ooO--(_)--Ooo--