From mboxrd@z Thu Jan 1 00:00:00 1970 From: vladimir.murzin@arm.com (Vladimir Murzin) Date: Tue, 10 Jan 2017 14:18:40 +0000 Subject: [RFC PATCH v4 0/5] ARM: Fix dma_alloc_coherent() and friends for NOMMU Message-ID: <1484057925-23586-1-git-send-email-vladimir.murzin@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 classes of cpu 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 2/5). It allows us to offload all bookkeeping on generic coherent DMA framework, and it is seems that it might be reused by other architectures like c6x and blackfin. 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 1/5 and PATCH 3/5). Thanks! [1] http://www.armlinux.org.uk/developer/patches/viewpatch.php?id=8633/1 Vladimir Murzin (5): dma: Add simple dma_noop_mmap 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 | 252 +++++++++++++++++++++ arch/arm/mm/dma-mapping.c | 26 +-- drivers/base/dma-coherent.c | 59 ++++- lib/dma-noop.c | 21 ++ 8 files changed, 335 insertions(+), 36 deletions(-) create mode 100644 arch/arm/mm/dma-mapping-nommu.c -- 2.0.0