drm/i915: stop abusing swiotlb_max_segment

swiotlb_max_segment used to return either the maximum size that swiotlb
could bounce, or for Xen PV PAGE_SIZE even if swiotlb could bounce buffer
larger mappings.  This made i915 on Xen PV work as it bypasses the
coherency aspect of the DMA API and can't cope with bounce buffering
and this avoided bounce buffering for the Xen/PV case.

So instead of adding this hack back, check for Xen/PV directly in i915
for the Xen case and otherwise use the proper DMA API helper to query
the maximum mapping size.

Replace swiotlb_max_segment() calls with dma_max_mapping_size().
In i915_gem_object_get_pages_internal() no longer consider max_segment
only if CONFIG_SWIOTLB is enabled. There can be other (iommu related)
causes of specific max segment sizes.

Fixes: a2daa27c0c61 ("swiotlb: simplify swiotlb_max_segment")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
[hch: added the Xen hack, rewrote the changelog]
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221020110308.1582518-1-hch@lst.de

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 1c60818ed2f1..9b7d101cf47a 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -129,7 +129,7 @@ static void i915_gem_object_userptr_drop_ref(struct drm_i915_gem_object *obj)
 static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
 {
 	const unsigned long num_pages = obj->base.size >> PAGE_SHIFT;
-	unsigned int max_segment = i915_sg_segment_size();
+	unsigned int max_segment = i915_sg_segment_size(obj->base.dev->dev);
 	struct sg_table *st;
 	unsigned int sg_page_sizes;
 	struct page **pvec;