[PATCH] drm: Remove SCATTERLIST_MAX_SEGMENT

* [PATCH] drm: Remove SCATTERLIST_MAX_SEGMENT
@ 2020-10-28 19:15 ` Jason Gunthorpe
  0 siblings, 0 replies; 13+ messages in thread
From: Jason Gunthorpe @ 2020-10-28 19:15 UTC (permalink / raw)
  To: David Airlie, Daniel Vetter, dri-devel, intel-gfx, Jani Nikula,
	Joonas Lahtinen, VMware Graphics, Maarten Lankhorst,
	Maxime Ripard, Rodrigo Vivi, Christoph Hellwig,
	Roland Scheidegger, Thomas Zimmermann
  Cc: Daniel Vetter, Thomas Hellstrom, Qian Cai, Gerd Hoffmann,
	Ursulin, Tvrtko

Since commit 9a40401cfa13 ("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>
---
 drivers/gpu/drm/drm_prime.c             | 4 ++--
 drivers/gpu/drm/i915/i915_scatterlist.h | 2 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c     | 3 +--
 include/linux/scatterlist.h             | 6 ------
 tools/testing/scatterlist/main.c        | 2 +-
 5 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index d6808f678db541..c3693e5e8b74b0 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -816,8 +816,8 @@ 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,
diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h b/drivers/gpu/drm/i915/i915_scatterlist.h
index b7b59328cb76ab..883dd8d09d6bf2 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.h
+++ b/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. */
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
index 31e3e5c9f36223..c1817f1a3006e0 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
@@ -792,8 +792,7 @@ 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",
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 36c47e7e66a203..6f70572b2938be 100644
--- a/include/linux/scatterlist.h
+++ b/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.
diff --git a/tools/testing/scatterlist/main.c b/tools/testing/scatterlist/main.c
index b2c7e9f7b8d3dc..d264bf853034bd 100644
--- a/tools/testing/scatterlist/main.c
+++ b/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 },
-- 
2.28.0

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