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SubjectRe: [PATCH v5 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU
Well, I've no objection to this, but it does need acks from other
people before I can apply it.

There's two patches that touch drivers/base that need Greg's ack.

I'm not sure what's happening with lib/dma-noop.c, there doesn't
appear to be a maintainer list for it, so I guess that's a
free-for-all.

On Thu, Jun 08, 2017 at 09:28:30AM +0100, Vladimir Murzin wrote:
> Ping!
>
> On 24/05/17 11:24, Vladimir Murzin wrote:
> > Short story:
> >
> > Without these patches coherent DMA is broken for András and Alexandre,
> > so they cannot safely enable DMA on their platforms.
> >
> > Patches have been circulated on a list since last year without much
> > attention to changes in dma-coherent.c and dma-noop.c. Meanwhile, ARM
> > bits have been reviewed and there is no strict objection to get them
> > merged. Unfortunately, applying only ARM bits doesn't help much and
> > the original issue would still exist.
> >
> > Please, let me know how to move with this fix forward?
> >
> > Long story:
> >
> > It seems 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 versions 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 any 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 at 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:
> > v4 -> v5
> > - rebased on v4.12-rc2
> > - updated description for CONFIG_ARM_DMA_MEM_BUFFERABLE
> >
> > 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 | 8 +-
> > 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, 359 insertions(+), 45 deletions(-)
> > create mode 100644 arch/arm/mm/dma-mapping-nommu.c
> >
>

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