[PATCH v3 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU
vladimir.murzin at arm.com
Thu Mar 23 02:26:23 PDT 2017
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.
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.
> Thanks for the patches!
>> On 2017. Mar 16., at 10:03, Vladimir Murzin <vladimir.murzin at 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  to allow mmap for NOMMU, his case is also addressed in this
>>> series (PATCH 1/7 and PATCH 2/7).
>>>  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>
>>> Cc: Doug Ledford <dledford at redhat.com>
>>> 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
>>> 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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