[RFC PATCH v6 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU
Vladimir Murzin
vladimir.murzin at arm.com
Mon Feb 6 01:07:10 PST 2017
Hi,
Can somebody help to get this series reviewed/merged?
Thanks!
Vladimir
On 31/01/17 11:30, Vladimir Murzin wrote:
> Gentle ping...
>
> On 26/01/17 16:42, 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
>>
>> Cc: Joerg Roedel <jroedel at suse.de>
>> Cc: Christian Borntraeger <borntraeger at de.ibm.com>
>> Cc: Michal Nazarewicz <mina86 at mina86.com>
>> Cc: Marek Szyprowski <m.szyprowski at samsung.com>
>> Cc: Alan Stern <stern at rowland.harvard.edu>
>> Cc: Yoshinori Sato <ysato at users.sourceforge.jp>
>> Cc: Rich Felker <dalias at libc.org>
>> Cc: Roger Quadros <rogerq at ti.com>
>> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
>> Cc: Rob Herring <robh+dt at kernel.org>
>> Cc: Mark Rutland <mark.rutland at arm.com>
>>
>> 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
>>
>
>
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