From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751980AbdBUKmL (ORCPT ); Tue, 21 Feb 2017 05:42:11 -0500 Received: from foss.arm.com ([217.140.101.70]:58202 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751325AbdBUKmE (ORCPT ); Tue, 21 Feb 2017 05:42:04 -0500 Subject: Re: [PATCH 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU To: linux-arm-kernel@lists.infradead.org References: <1487152792-34214-1-git-send-email-vladimir.murzin@arm.com> Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, robin.murphy@arm.com, kbuild-all@01.org, linux@armlinux.org.uk, jroedel@suse.de, borntraeger@de.ibm.com, mina86@mina86.com, m.szyprowski@samsung.com, stern@rowland.harvard.edu, ysato@users.sourceforge.jp, dalias@libc.org, rogerq@ti.com, gregkh@linuxfoundation.org, Rob Herring , Mark Rutland From: Vladimir Murzin Message-ID: Date: Tue, 21 Feb 2017 10:41:49 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <1487152792-34214-1-git-send-email-vladimir.murzin@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Gentle ping! Cc: Joerg Roedel Cc: Christian Borntraeger Cc: Michal Nazarewicz Cc: Marek Szyprowski Cc: Alan Stern Cc: Yoshinori Sato Cc: Rich Felker Cc: Roger Quadros Cc: Greg Kroah-Hartman Cc: Rob Herring Cc: Mark Rutland On 15/02/17 09:59, Vladimir Murzin wrote: > Hi, > > It seem that addition of cache support for M-class CPUs uncovered > latent bug in DMA usage. NOMMU memory model has been treated as being > always consistent; however, for R/M CPU classes memory can be covered > by MPU which in turn might configure RAM as Normal i.e. bufferable and > cacheable. It breaks dma_alloc_coherent() and friends, since data can > stuck in caches now or be buffered. > > This patch set is trying to address the issue by providing region of > memory suitable for consistent DMA operations. It is supposed that > such region is marked by MPU as non-cacheable. Robin suggested to > advertise such memory as reserved shared-dma-pool, rather then using > homebrew command line option, and extend dma-coherent to provide > default DMA area in the similar way as it is done for CMA (PATCH > 4/7). It allows us to offload all bookkeeping on generic coherent DMA > framework, and it seems that it might be reused by other architectures > like c6x and blackfin. > > While reviewing/testing previous vesrions of the patch set it turned > out that dma-coherent does not take into account "dma-ranges" device > tree property, so it is addressed in PATCH 3/7. > > For ARM, dedicated DMA region is required for cases other than: > - MMU/MPU is off > - cpu is v7m w/o cache support > - device is coherent > > In case one of the above conditions is true dma operations are forced > to be coherent and wired with dma_noop_ops. > > To make life easier NOMMU dma operations are kept in separate > compilation unit. > > Since the issue was reported in the same time as Benjamin sent his > patch [1] to allow mmap for NOMMU, his case is also addressed in this > series (PATCH 1/7 and PATCH 2/7). > > Thanks! > > [1] http://www.armlinux.org.uk/developer/patches/viewpatch.php?id=8633/1 > > Changelog: > RFC v6 -> v1 > - dropped RFC tag > - added Alexandre's Tested-by > > Vladimir Murzin (7): > dma: Take into account dma_pfn_offset > dma: Add simple dma_noop_mmap > drivers: dma-coherent: Account dma_pfn_offset when used with device > tree > drivers: dma-coherent: Introduce default DMA pool > ARM: NOMMU: Introduce dma operations for noMMU > ARM: NOMMU: Set ARM_DMA_MEM_BUFFERABLE for M-class cpus > ARM: dma-mapping: Remove traces of NOMMU code > > .../bindings/reserved-memory/reserved-memory.txt | 3 + > arch/arm/include/asm/dma-mapping.h | 3 +- > arch/arm/mm/Kconfig | 2 +- > arch/arm/mm/Makefile | 5 +- > arch/arm/mm/dma-mapping-nommu.c | 253 +++++++++++++++++++++ > arch/arm/mm/dma-mapping.c | 26 +-- > drivers/base/dma-coherent.c | 76 ++++++- > lib/dma-noop.c | 29 ++- > 8 files changed, 356 insertions(+), 41 deletions(-) > create mode 100644 arch/arm/mm/dma-mapping-nommu.c >