Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752103AbdCPJEN (ORCPT ); Thu, 16 Mar 2017 05:04:13 -0400 Received: from foss.arm.com ([217.140.101.70]:59326 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751428AbdCPJEK (ORCPT ); Thu, 16 Mar 2017 05:04:10 -0400 Subject: Re: [PATCH v3 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU To: linux-arm-kernel@lists.infradead.org References: <1489137839-549-1-git-send-email-vladimir.murzin@arm.com> Cc: Mark Rutland , Roger Quadros , Joerg Roedel , alexandre.torgue@st.com, Yoshinori Sato , Greg Kroah-Hartman , linux@armlinux.org.uk, Michal Nazarewicz , linux-kernel@vger.kernel.org, Christian Borntraeger , Doug Ledford , Rich Felker , Alan Stern , kbuild-all@01.org, benjamin.gaignard@linaro.org, Rob Herring , akpm@linux-foundation.org, Marek Szyprowski , robin.murphy@arm.com, sza@esh.hu From: Vladimir Murzin Message-ID: <90e219f3-7139-c11c-a635-509173d4148a@arm.com> Date: Thu, 16 Mar 2017 09:03:35 +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: <1489137839-549-1-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 Content-Length: 3965 Lines: 93 Gentle ping! On 10/03/17 09:23, Vladimir Murzin wrote: > 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 > > 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 > Cc: Doug Ledford > > Changelog: > v2 -> v3 > - fixed warnings reported by Alexandre and kbuild robot > > v1 -> v2 > - rebased on v4.11-rc1 > - added Robin's Reviewed-by > - dedicated flag is introduced to use dev->dma_pfn_offset > rather than mem->device_base in case memory region is > configured via device tree (so Tested-by discarded there) > > 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/Kconfig | 1 + > arch/arm/include/asm/dma-mapping.h | 2 +- > arch/arm/mm/Kconfig | 2 +- > arch/arm/mm/Makefile | 5 +- > arch/arm/mm/dma-mapping-nommu.c | 253 +++++++++++++++++++++ > arch/arm/mm/dma-mapping.c | 29 +-- > drivers/base/dma-coherent.c | 74 +++++- > lib/dma-noop.c | 29 ++- > 9 files changed, 354 insertions(+), 44 deletions(-) > create mode 100644 arch/arm/mm/dma-mapping-nommu.c >