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Message-ID: <20170523200439.GE22219@n2100.armlinux.org.uk>
Date: Tue, 23 May 2017 21:04:39 +0100
From: Russell King - ARM Linux <linux@...linux.org.uk>
To: Vladimir Murzin <vladimir.murzin@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
Mark Rutland <mark.rutland@....com>,
Joerg Roedel <jroedel@...e.de>, sza@....hu,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
alexandre.torgue@...com, gregkh@...uxfoundation.org,
linux-kernel@...r.kernel.org,
Michal Nazarewicz <mina86@...a86.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Doug Ledford <dledford@...hat.com>,
Rich Felker <dalias@...c.org>, arnd@...db.de,
kbuild-all@...org, Rob Herring <robh+dt@...nel.org>,
Alan Stern <stern@...land.harvard.edu>,
akpm@...ux-foundation.org,
Marek Szyprowski <m.szyprowski@...sung.com>,
robin.murphy@....com, Roger Quadros <rogerq@...com>
Subject: Re: [PATCH v4 0/7] ARM: Fix dma_alloc_coherent() and friends for
NOMMU
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@...e.de>
> >> Cc: Christian Borntraeger <borntraeger@...ibm.com>
> >> Cc: Michal Nazarewicz <mina86@...a86.com>
> >> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> >> Cc: Alan Stern <stern@...land.harvard.edu>
> >> Cc: Yoshinori Sato <ysato@...rs.sourceforge.jp>
> >> Cc: Rich Felker <dalias@...c.org>
> >> Cc: Roger Quadros <rogerq@...com>
> >> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> >> Cc: Rob Herring <robh+dt@...nel.org>
> >> Cc: Mark Rutland <mark.rutland@....com>
> >> Cc: Doug Ledford <dledford@...hat.com>
> >>
> >> 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@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >
>
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