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    SubjectRe: [PATCH v3 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU
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    On 22/03/17 12:23, Szemző András wrote:
    > 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.

    Much appreciated!

    Russell, Andrew, Greg, any advise on how to get this series merged? Patches
    has been circulated on a list since December last year and without them András
    and Alexandre cannot safely enable DMA on their platforms.

    Cheers
    Vladimir

    >
    > Thanks for the patches!
    >
    > Andras
    >
    >> On 2017. Mar 16., at 10:03, Vladimir Murzin <vladimir.murzin@arm.com> 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 <jroedel@suse.de>
    >>> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
    >>> Cc: Michal Nazarewicz <mina86@mina86.com>
    >>> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
    >>> Cc: Alan Stern <stern@rowland.harvard.edu>
    >>> Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
    >>> Cc: Rich Felker <dalias@libc.org>
    >>> Cc: Roger Quadros <rogerq@ti.com>
    >>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    >>> Cc: Rob Herring <robh+dt@kernel.org>
    >>> Cc: Mark Rutland <mark.rutland@arm.com>
    >>> Cc: Doug Ledford <dledford@redhat.com>
    >>>
    >>> 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
    >>>
    >>
    >
    >

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