linux-kernel - [RFC v2] Change dma_attrs from bitfield to unsigned long

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Date:	Mon, 30 May 2016 13:54:05 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Joerg Roedel <joro@...tes.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Hocko <mhocko@...e.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Arnd Bergmann <arnd@...db.de>,
	Andy Lutomirski <luto@...nel.org>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	xen-devel@...ts.xenproject.org, dri-devel@...ts.freedesktop.org,
	linux-samsung-soc@...r.kernel.org, iommu@...ts.linux-foundation.org
Cc:	hch@...radead.org, sstabellini@...nel.org,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: [RFC v2] Change dma_attrs from bitfield to unsigned long

Hi,


This is second attempt to bring some safeness to dma_attrs.
In v1 [0] I added const to data pointed by attrs. However Christoph
Hellwig suggested getting rid of struct dma_attrs in favor of
some simpler data type.


Benefits of unsigned long for dma_attrs:
1. This is just simpler.  Both in terms of reading the code and setting
   attributes.  Instead of initializing local attributes on the stack and
   passing pointer to it to dma_set_attr(), just set the bits.

2. It brings safeness and checking for const correctness because the
   attributes are passed by value.


The problem is that the patch touches the dma-mapping API so all
the users have to be converted (ARM and ARM64 as of now).

Any ideas to split it per smaller patches?

The work is not finished yet, I would rather get some feedback before
progressing further.


Best regards,
Krzysztof


Krzysztof Kozlowski (1):
  dma-mapping: Use unsigned long for dma_attrs

 Documentation/DMA-API.txt                 |   2 +-
 Documentation/DMA-attributes.txt          |   2 +-
 arch/arm/include/asm/dma-mapping.h        |  13 ++--
 arch/arm/include/asm/xen/page-coherent.h  |  16 ++---
 arch/arm/mm/dma-mapping.c                 |  82 +++++++++++------------
 arch/arm/xen/mm.c                         |   4 +-
 arch/arm64/mm/dma-mapping.c               |  57 ++++++++--------
 drivers/gpu/drm/exynos/exynos_drm_fbdev.c |   2 +-
 drivers/gpu/drm/exynos/exynos_drm_g2d.c   |   1 -
 drivers/gpu/drm/exynos/exynos_drm_gem.c   |  20 +++---
 drivers/gpu/drm/exynos/exynos_drm_gem.h   |   2 +-
 drivers/iommu/dma-iommu.c                 |   6 +-
 drivers/xen/swiotlb-xen.c                 |  14 ++--
 include/linux/dma-attrs.h                 |  71 --------------------
 include/linux/dma-iommu.h                 |   6 +-
 include/linux/dma-mapping.h               | 105 +++++++++++++++++-------------
 include/linux/swiotlb.h                   |  10 +--
 include/xen/swiotlb-xen.h                 |  12 ++--
 lib/dma-noop.c                            |   9 +--
 lib/swiotlb.c                             |  13 ++--
 20 files changed, 195 insertions(+), 252 deletions(-)
 delete mode 100644 include/linux/dma-attrs.h

-- 
1.9.1