[PATCH] 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 all the pages in the SG list and
map them one by one. This ensures all the pages of current SG list are mapped.
Next SG list of the same buffer will be mapped when page fault occurs for
the offset belongs to that list.

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

Signed-off-by: Rahul Sharma <rahul.sharma at samsung.com>
---
 drivers/gpu/drm/exynos/exynos_drm_gem.c |   34 +++++++++++++++++++++++++++---
 1 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
index 7057729..d2d6188 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
@@ -95,17 +95,43 @@ 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;
+	unsigned int phys_addr;
+	int ret, i;
 
 	if (exynos_gem_obj->flags & EXYNOS_BO_NONCONTIG) {
 		if (!buf->pages)
 			return -EINTR;
 
-		pfn = page_to_pfn(buf->pages[page_offset++]);
-	} else
+		sgl = buf->sgt->sgl;
+		for_each_sg(buf->sgt->sgl, sgl, buf->sgt->nents, i) {
+			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;
+		}
+
+		phys_addr = sg_phys(sgl);
+
+		for (i = 0; i < (sgl->length >> PAGE_SHIFT); i++) {
+			pfn = __phys_to_pfn(phys_addr + (i << PAGE_SHIFT));
+			ret = vm_insert_mixed(vma, f_vaddr + (i << PAGE_SHIFT),
+						pfn);
+			if (ret < 0) {
+				DRM_ERROR("failed to map page.\n");
+				return ret;
+			}
+		}
+		return 0;
+	} else {
 		pfn = (buf->dma_addr >> PAGE_SHIFT) + page_offset;
-
-	return vm_insert_mixed(vma, f_vaddr, pfn);
+		return vm_insert_mixed(vma, f_vaddr, pfn);
+	}
 }
 
 static int exynos_drm_gem_handle_create(struct drm_gem_object *obj,
-- 
1.7.0.4