[PATCH] drm: modify pages_to_sg prime helper to create optimized SG table

[Rahul Sharma]

It fixes the issue arises due to passing 'nr_pages' in place of 'nents' to
sg_alloc_table. When ARM_HAS_SG_CHAIN is disabled, it is causing failure in
creating SG table for the buffers having more than 204 physical pages i.e.
equal to SG_MAX_SINGLE_ALLOC.

When using sg_alloc_table_from_pages interface, in place of sg_alloc_table,
page list will be passes to get each contiguous section which is represented
by a single entry in the table. For a Contiguous Buffer, number of entries
should be equal to 1.

Following check is causing the failure which is not applicable for Non-Contig
buffers:

	if (WARN_ON_ONCE(nents > max_ents))
		return -EINVAL;

Above patch is well tested for EXYNOS4 and EXYNOS5 for with/wihtout IOMMU
supprot. NOUVEAU and RADEON platforms also depends on drm_prime_pages_to_sg
helper function.

This set is base on "exynos-drm-fixes" branch at
http://git.kernel.org/?p=linux/kernel/git/daeinki/drm-exynos.git

Signed-off-by: Rahul Sharma <rahul.sharma at samsung.com>
---
 drivers/gpu/drm/drm_prime.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 7f12573..072ee08 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -217,21 +217,17 @@ int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
 struct sg_table *drm_prime_pages_to_sg(struct page **pages, int nr_pages)
 {
 	struct sg_table *sg = NULL;
-	struct scatterlist *iter;
-	int i;
 	int ret;
 
 	sg = kmalloc(sizeof(struct sg_table), GFP_KERNEL);
 	if (!sg)
 		goto out;
 
-	ret = sg_alloc_table(sg, nr_pages, GFP_KERNEL);
+	ret = sg_alloc_table_from_pages(sg, pages, nr_pages, 0,
+				nr_pages << PAGE_SHIFT, GFP_KERNEL);
 	if (ret)
 		goto out;
 
-	for_each_sg(sg->sgl, iter, nr_pages, i)
-		sg_set_page(iter, pages[i], PAGE_SIZE, 0);
-
 	return sg;
 out:
 	kfree(sg);
-- 
1.8.0