linux-kernel - Re: [PATCH v5 0/7] ARM: Fix dma_alloc_coherent() and friends for NOMMU

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Date:   Tue, 20 Jun 2017 13:59:10 +0100
From:   Vladimir Murzin <vladimir.murzin@....com>
To:     hch@....de
Cc:     gregkh@...uxfoundation.org, Mark Rutland <mark.rutland@....com>,
        Joerg Roedel <jroedel@...e.de>, sza@....hu, arnd@...db.de,
        alexandre.torgue@...com, linux-kernel@...r.kernel.org,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Michal Nazarewicz <mina86@...a86.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Doug Ledford <dledford@...hat.com>,
        Rich Felker <dalias@...c.org>,
        Alan Stern <stern@...land.harvard.edu>, kbuild-all@...org,
        benjamin.gaignard@...aro.org, Rob Herring <robh+dt@...nel.org>,
        akpm@...ux-foundation.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        robin.murphy@....com, linux-arm-kernel@...ts.infradead.org,
        Roger Quadros <rogerq@...com>
Subject: Re: [PATCH v5 0/7] ARM: Fix dma_alloc_coherent() and friends for
 NOMMU

+Christoph since he is trying to consolidate work in this area [1].

Christoph, any chance you can look into patches touching
dma-{coherent,noop}.c?

[1] https://patchwork.ozlabs.org/patch/778254/

Thanks!
Vladimir

On 15/06/17 08:25, Vladimir Murzin wrote:
> Greg?
> 
> On 08/06/17 17:25, Russell King - ARM Linux wrote:
>> 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@...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:
>>>> 	    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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