drm: Remove SCATTERLIST_MAX_SEGMENT

Since commit 9a40401c ("lib/scatterlist: Do not limit max_segment to
PAGE_ALIGNED values") the max_segment input to sg_alloc_table_from_pages()
does not have to be any special value. The new algorithm will always
create something less than what the user provides. Thus eliminate this
confusing constant.

- vmwgfx should use the HW capability, not mix in the OS page size for
  calling dma_set_max_seg_size()

- i915 uses i915_sg_segment_size() both for sg_alloc_table_from_pages
  and for some open coded sgl construction. This doesn't change the value
  since rounddown(size, UINT_MAX) == SCATTERLIST_MAX_SEGMENT

- drm_prime_pages_to_sg uses it as a default if max_segment is zero,
  UINT_MAX is fine to use directly.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Qian Cai <cai@lca.pw>
Cc: "Ursulin, Tvrtko" <tvrtko.ursulin@intel.com>
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/0-v1-44733fccd781+13d-rm_scatterlist_max_jgg@nvidia.com

drivers/gpu/drm/drm_prime.c

@@ -820,8 +820,8 @@ struct sg_table *drm_prime_pages_to_sg(struct drm_device *dev,
 
 	if (dev)
 		max_segment = dma_max_mapping_size(dev->dev);
-	if (max_segment == 0 || max_segment > SCATTERLIST_MAX_SEGMENT)
-		max_segment = SCATTERLIST_MAX_SEGMENT;
+	if (max_segment == 0)
+		max_segment = UINT_MAX;
 	sge = __sg_alloc_table_from_pages(sg, pages, nr_pages, 0,
 					  nr_pages << PAGE_SHIFT,
 					  max_segment,

drivers/gpu/drm/i915/i915_scatterlist.h

@@ -112,7 +112,7 @@ static inline unsigned int i915_sg_segment_size(void)
 	unsigned int size = swiotlb_max_segment();
 
 	if (size == 0)
-		return SCATTERLIST_MAX_SEGMENT;
+		size = UINT_MAX;
 
 	size = rounddown(size, PAGE_SIZE);
 	/* swiotlb_max_segment_size can return 1 byte when it means one page. */

drivers/gpu/drm/vmwgfx/vmwgfx_drv.c

@@ -794,8 +794,7 @@ static int vmw_driver_load(struct drm_device *dev, unsigned long chipset)
 	if (unlikely(ret != 0))
 		goto out_err0;
 
-	dma_set_max_seg_size(dev->dev, min_t(unsigned int, U32_MAX & PAGE_MASK,
-					     SCATTERLIST_MAX_SEGMENT));
+	dma_set_max_seg_size(dev->dev, U32_MAX);
 
 	if (dev_priv->capabilities & SVGA_CAP_GMR2) {
 		DRM_INFO("Max GMR ids is %u\n",

include/linux/scatterlist.h

@@ -18,12 +18,6 @@ struct scatterlist {
 #endif
 };
 
-/*
- * Since the above length field is an unsigned int, below we define the maximum
- * length in bytes that can be stored in one scatterlist entry.
- */
-#define SCATTERLIST_MAX_SEGMENT (UINT_MAX & PAGE_MASK)
-
 /*
  * These macros should be used after a dma_map_sg call has been done
  * to get bus addresses of each of the SG entries and their lengths.

tools/testing/scatterlist/main.c

@@ -50,7 +50,7 @@ static void fail(struct test *test, struct sg_table *st, const char *cond)
 
 int main(void)
 {
-	const unsigned int sgmax = SCATTERLIST_MAX_SEGMENT;
+	const unsigned int sgmax = UINT_MAX;
 	struct test *test, tests[] = {
 		{ -EINVAL, 1, pfn(0), PAGE_SIZE, PAGE_SIZE + 1, 1 },
 		{ -EINVAL, 1, pfn(0), PAGE_SIZE, 0, 1 },