Re: [PATCH v4 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU

[Russell King - ARM Linux]

On Mon, May 15, 2017 at 09:52:58AM +0100, Vladimir Murzin wrote:
> Ping again...

Apart from the one comment, the ARM bits look fine to me - but I'm
not saying anything about the lib/dma-noop.c or the drivers/base
changes.

What's the dependency between the ARM bits and those bits?

> On 02/05/17 09:32, Vladimir Murzin wrote:
> > Gentle ping!
> > 
> > On 24/04/17 11:16, 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@xxxxxxx>
> >> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> >> Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
> >> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> >> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> >> Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
> >> Cc: Rich Felker <dalias@xxxxxxxx>
> >> Cc: Roger Quadros <rogerq@xxxxxx>
> >> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> >> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> >> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> >> Cc: Doug Ledford <dledford@xxxxxxxxxx>
> >>
> >> Changelog:
> >> 	    v3 -> v4
> >> 	       - rebased on v4.11-rc7
> >> 	       - made CONFIG_ARM_DMA_MEM_BUFFERABLE optional for CPU_V7M
> >> 	       - added Arnd's Acked-by
> >>
> >> 	    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                                |   4 +-
> >>  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, 355 insertions(+), 45 deletions(-)
> >>  create mode 100644 arch/arm/mm/dma-mapping-nommu.c
> >>
> > 
> > 
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> > 
> 

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