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Tvrtko Ursulin authored
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: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
References: 85d1225e ("drm/i915: Introduce & use new lightweight SGL iterators")
References: b31144c0 ("drm/i915: Micro-optimise gen6_ppgtt_insert_entries()")
Reported-by: default avatarTom 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: default avatarLogan Gunthorpe <logang@deltatee.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201006092508.1064287-1-tvrtko.ursulin@linux.intel.com
8a473dba
Linux kernel
============

There are several guides for kernel developers and users. These guides can
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