[PATCH v1] drm: exynos: fix for mapping non contig dma buffers

[Rahul Sharma]

This patch fixes the problem of mapping gem objects which are non-contigous
dma buffers. These buffers are described using SG table and SG lists. Each
valid SG List is pointing to a single page or group of pages which are
physically contigous.

Current implementation just maps the first page of each SG List and leave
the other pages unmapped, leading to a crash.

Given solution finds the page struct for the faulting page through parsing SG
table and map it.

This patch is based on branch exynos-drm-next-iommu at
git://git.kernel.org/pub/scm/linux/kernel/git/daeinki/drm-exynos.git

v1:
1) instead of mapping whole section, mapping single page.

Signed-off-by: Rahul Sharma <rahul.sharma at samsung.com>
---
 drivers/gpu/drm/exynos/exynos_drm_gem.c |   22 ++++++++++++++++++++--
 1 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
index 8cb6824..c557ac7 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
@@ -95,13 +95,31 @@ static int exynos_drm_gem_map_buf(struct drm_gem_object *obj,
 {
 	struct exynos_drm_gem_obj *exynos_gem_obj = to_exynos_gem_obj(obj);
 	struct exynos_drm_gem_buf *buf = exynos_gem_obj->buffer;
+	struct scatterlist *sgl;
 	unsigned long pfn;
+	int i;
 
 	if (exynos_gem_obj->flags & EXYNOS_BO_NONCONTIG) {
-		if (!buf->pages)
+		if (!buf->sgt)
 			return -EINTR;
 
-		pfn = page_to_pfn(buf->pages[page_offset++]);
+		sgl = buf->sgt->sgl;
+		for_each_sg(buf->sgt->sgl, sgl, buf->sgt->nents, i) {
+			if (!sgl) {
+				DRM_ERROR("invalid SG table\n");
+				return -EINTR;
+			}
+			if (page_offset < (sgl->length >> PAGE_SHIFT))
+				break;
+			page_offset -=	(sgl->length >> PAGE_SHIFT);
+		}
+
+		if (i >= buf->sgt->nents) {
+			DRM_ERROR("invalid page offset\n");
+			return -EINVAL;
+		}
+
+		pfn = __phys_to_pfn(sg_phys(sgl)) + page_offset;
 	} else
 		pfn = (buf->dma_addr >> PAGE_SHIFT) + page_offset;
 
-- 
1.7.0.4