linux-kernel - Re: [PATCH v2] lib/scatterlist: Provide a DMA page iterator

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Date:   Mon, 11 Feb 2019 15:26:54 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Stone <daniel@...ishbar.org>, "hch@....de" <hch@....de>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yong.zhi@...el.com" <yong.zhi@...el.com>,
        "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "bingbu.cao@...el.com" <bingbu.cao@...el.com>,
        "tian.shu.qiu@...el.com" <tian.shu.qiu@...el.com>,
        "shiraz.saleem@...el.com" <shiraz.saleem@...el.com>,
        "sakari.ailus@...ux.intel.com" <sakari.ailus@...ux.intel.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v2] lib/scatterlist: Provide a DMA page iterator

On Thu, Feb 07, 2019 at 10:26:52PM +0000, Jason Gunthorpe wrote:
> Commit 2db76d7c3c6d ("lib/scatterlist: sg_page_iter: support sg lists w/o
> backing pages") introduced the sg_page_iter_dma_address() function without
> providing a way to use it in the general case. If the sg_dma_len() is not
> equal to the sg length callers cannot safely use the
> for_each_sg_page/sg_page_iter_dma_address combination.
> 
> Resolve this API mistake by providing a DMA specific iterator,
> for_each_sg_dma_page(), that uses the right length so
> sg_page_iter_dma_address() works as expected with all sglists.
> 
> A new iterator type is introduced to provide compile-time safety against
> wrongly mixing accessors and iterators.
> 
> Acked-by: Christoph Hellwig <hch@....de> (for scatterlist)
> Signed-off-by: Jason Gunthorpe <jgg@...lanox.com>
> Acked-by: Thomas Hellstrom <thellstrom@...are.com>
> ---
>  .clang-format                              |  1 +
>  drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c |  8 +++-
>  drivers/media/pci/intel/ipu3/ipu3-cio2.c   |  4 +-
>  include/linux/scatterlist.h                | 49 ++++++++++++++++++----
>  lib/scatterlist.c                          | 26 ++++++++++++
>  5 files changed, 76 insertions(+), 12 deletions(-)

Applied to rdma.git's for-next, thanks everyone.

Jason