drm/i915: Replace the array of pages with a scatterlist

Rather than have multiple data structures for describing our page layout
in conjunction with the array of pages, we can migrate all users over to
a scatterlist.

One major advantage, other than unifying the page tracking structures,
this offers is that we replace the vmalloc'ed array (which can be up to
a megabyte in size) with a chain of individual pages which helps reduce
memory pressure.

The disadvantage is that we then do not have a simple array to iterate,
or to access randomly. The common case for this is in the relocation
processing, which will typically fit within a single scatterlist page
and so be almost the same cost as the simple array. For iterating over
the array, the extra function call could be optimised away, but in
reality is an insignificant cost of either binding the pages, or
performing the pwrite/pread.

v2: Fix drm_clflush_sg() to not invoke wbinvd as well! And fix the
trivial compile error from rebasing.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 66 insertions, 33 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
index eca4726..4bb1b94 100644
--- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
@@ -28,33 +28,57 @@
 #include <linux/dma-buf.h>
 
 static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachment,
-				      enum dma_data_direction dir)
+					     enum dma_data_direction dir)
 {
 	struct drm_i915_gem_object *obj = attachment->dmabuf->priv;
-	struct drm_device *dev = obj->base.dev;
-	int npages = obj->base.size / PAGE_SIZE;
-	struct sg_table *sg;
-	int ret;
-	int nents;
+	struct sg_table *st;
+	struct scatterlist *src, *dst;
+	int ret, i;
 
-	ret = i915_mutex_lock_interruptible(dev);
+	ret = i915_mutex_lock_interruptible(obj->base.dev);
 	if (ret)
 		return ERR_PTR(ret);
 
 	ret = i915_gem_object_get_pages(obj);
 	if (ret) {
-		sg = ERR_PTR(ret);
+		st = ERR_PTR(ret);
+		goto out;
+	}
+
+	/* Copy sg so that we make an independent mapping */
+	st = kmalloc(sizeof(struct sg_table), GFP_KERNEL);
+	if (st == NULL) {
+		st = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+
+	ret = sg_alloc_table(st, obj->pages->nents, GFP_KERNEL);
+	if (ret) {
+		kfree(st);
+		st = ERR_PTR(ret);
+		goto out;
+	}
+
+	src = obj->pages->sgl;
+	dst = st->sgl;
+	for (i = 0; i < obj->pages->nents; i++) {
+		sg_set_page(dst, sg_page(src), PAGE_SIZE, 0);
+		dst = sg_next(dst);
+		src = sg_next(src);
+	}
+
+	if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
+		sg_free_table(st);
+		kfree(st);
+		st = ERR_PTR(-ENOMEM);
 		goto out;
 	}
 
-	/* link the pages into an SG then map the sg */
-	sg = drm_prime_pages_to_sg(obj->pages, npages);
-	nents = dma_map_sg(attachment->dev, sg->sgl, sg->nents, dir);
 	i915_gem_object_pin_pages(obj);
 
 out:
-	mutex_unlock(&dev->struct_mutex);
-	return sg;
+	mutex_unlock(&obj->base.dev->struct_mutex);
+	return st;
 }
 
 static void i915_gem_unmap_dma_buf(struct dma_buf_attachment *attachment,
@@ -80,7 +104,9 @@ static void *i915_gem_dmabuf_vmap(struct dma_buf *dma_buf)
 {
 	struct drm_i915_gem_object *obj = dma_buf->priv;
 	struct drm_device *dev = obj->base.dev;
-	int ret;
+	struct scatterlist *sg;
+	struct page **pages;
+	int ret, i;
 
 	ret = i915_mutex_lock_interruptible(dev);
 	if (ret)
@@ -92,22 +118,33 @@ static void *i915_gem_dmabuf_vmap(struct dma_buf *dma_buf)
 	}
 
 	ret = i915_gem_object_get_pages(obj);
-	if (ret) {
-		mutex_unlock(&dev->struct_mutex);
-		return ERR_PTR(ret);
-	}
+	if (ret)
+		goto error;
 
-	obj->dma_buf_vmapping = vmap(obj->pages, obj->base.size / PAGE_SIZE, 0, PAGE_KERNEL);
-	if (!obj->dma_buf_vmapping) {
-		DRM_ERROR("failed to vmap object\n");
-		goto out_unlock;
-	}
+	ret = -ENOMEM;
+
+	pages = drm_malloc_ab(obj->pages->nents, sizeof(struct page *));
+	if (pages == NULL)
+		goto error;
+
+	for_each_sg(obj->pages->sgl, sg, obj->pages->nents, i)
+		pages[i] = sg_page(sg);
+
+	obj->dma_buf_vmapping = vmap(pages, obj->pages->nents, 0, PAGE_KERNEL);
+	drm_free_large(pages);
+
+	if (!obj->dma_buf_vmapping)
+		goto error;
 
 	obj->vmapping_count = 1;
 	i915_gem_object_pin_pages(obj);
 out_unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return obj->dma_buf_vmapping;
+
+error:
+	mutex_unlock(&dev->struct_mutex);
+	return ERR_PTR(ret);
 }
 
 static void i915_gem_dmabuf_vunmap(struct dma_buf *dma_buf, void *vaddr)
@@ -184,22 +221,19 @@ static const struct dma_buf_ops i915_dmabuf_ops =  {
 };
 
 struct dma_buf *i915_gem_prime_export(struct drm_device *dev,
-				struct drm_gem_object *gem_obj, int flags)
+				      struct drm_gem_object *gem_obj, int flags)
 {
 	struct drm_i915_gem_object *obj = to_intel_bo(gem_obj);
 
-	return dma_buf_export(obj, &i915_dmabuf_ops,
-						  obj->base.size, 0600);
+	return dma_buf_export(obj, &i915_dmabuf_ops, obj->base.size, 0600);
 }
 
 struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
-				struct dma_buf *dma_buf)
+					     struct dma_buf *dma_buf)
 {
 	struct dma_buf_attachment *attach;
 	struct sg_table *sg;
 	struct drm_i915_gem_object *obj;
-	int npages;
-	int size;
 	int ret;
 
 	/* is this one of own objects? */
@@ -223,21 +257,19 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
 		goto fail_detach;
 	}
 
-	size = dma_buf->size;
-	npages = size / PAGE_SIZE;
-
 	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
 	if (obj == NULL) {
 		ret = -ENOMEM;
 		goto fail_unmap;
 	}
 
-	ret = drm_gem_private_object_init(dev, &obj->base, size);
+	ret = drm_gem_private_object_init(dev, &obj->base, dma_buf->size);
 	if (ret) {
 		kfree(obj);
 		goto fail_unmap;
 	}
 
+	obj->has_dma_mapping = true;
 	obj->sg_table = sg;
 	obj->base.import_attach = attach;
 
@@ -249,3 +281,4 @@ fail_detach:
 	dma_buf_detach(dma_buf, attach);
 	return ERR_PTR(ret);
 }
+