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swiotlb: Export swiotlb_max_segment to users

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So they can figure out what is the optimal number of pages
that can be contingously stitched together without fear of
bounce buffer.

We also expose an mechanism for sub-users of SWIOTLB API, such
as Xen-SWIOTLB to set the max segment value. And lastly
if swiotlb=force is set (which mandates we bounce buffer everything)
we set max_segment so at least we can bounce buffer one 4K page
instead of a giant 512KB one for which we may not have space.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reported-and-Tested-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Konrad Rzeszutek Wilk
2016-12-20 10:02:02 -05:00
committed by Konrad Rzeszutek Wilk
parent fff5d99225
commit 7453c549f5
4 changed files with 34 additions and 10 deletions
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11
drivers/gpu/drm/i915/i915_gem.c
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@@ -2290,15 +2290,6 @@ unlock:
mutex_unlock(&obj->mm.lock);
}
static unsigned int swiotlb_max_size(void)
{
#if IS_ENABLED(CONFIG_SWIOTLB)
return rounddown(swiotlb_nr_tbl() << IO_TLB_SHIFT, PAGE_SIZE);
#else
return 0;
#endif
}
static void i915_sg_trim(struct sg_table *orig_st)
{
struct sg_table new_st;
@@ -2345,7 +2336,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
GEM_BUG_ON(obj->base.read_domains & I915_GEM_GPU_DOMAINS);
GEM_BUG_ON(obj->base.write_domain & I915_GEM_GPU_DOMAINS);
max_segment = swiotlb_max_size();
max_segment = swiotlb_max_segment();
if (!max_segment)
max_segment = rounddown(UINT_MAX, PAGE_SIZE);