I’ve tested this v3 version on my Atmel armv7m board with several drivers with DMA and enabled caches, and I’ve not seen any issues.
You can add my Tested-by. Thanks for the patches! Andras > On 2017. Mar 16., at 10:03, Vladimir Murzin <[email protected]> wrote: > > 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 <[email protected]> >> Cc: Christian Borntraeger <[email protected]> >> Cc: Michal Nazarewicz <[email protected]> >> Cc: Marek Szyprowski <[email protected]> >> Cc: Alan Stern <[email protected]> >> Cc: Yoshinori Sato <[email protected]> >> Cc: Rich Felker <[email protected]> >> Cc: Roger Quadros <[email protected]> >> Cc: Greg Kroah-Hartman <[email protected]> >> Cc: Rob Herring <[email protected]> >> Cc: Mark Rutland <[email protected]> >> Cc: Doug Ledford <[email protected]> >> >> 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 >> >
