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When walking DMA mapped scatterlists sg_dma_len has to be used since it can be different (coalesced) from the backing store entry. This also means we have to end the walk when encountering a zero length DMA entry and cannot rely on the normal sg list end marker. Both issues were there in theory for some time but were hidden by the fact Intel IOMMU driver was never coalescing entries. As there are ongoing efforts to change this we need to start handling it. v2: * Use unsigned int for local storing sg_dma_len. (Logan) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> References:85d1225ec0("drm/i915: Introduce & use new lightweight SGL iterators") References:b31144c0da("drm/i915: Micro-optimise gen6_ppgtt_insert_entries()") Reported-by: Tom Murphy <murphyt7@tcd.ie> Suggested-by: Tom Murphy <murphyt7@tcd.ie> # __sgt_iter Suggested-by: Logan Gunthorpe <logang@deltatee.com> # __sgt_iter Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Lu Baolu <baolu.lu@linux.intel.com> Reviewed-by: Logan Gunthorpe <logang@deltatee.com> Link: https://patchwork.freedesktop.org/patch/msgid/20201006092508.1064287-1-tvrtko.ursulin@linux.intel.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.