Use dummy_read_page for unpopulated kernel-allocated ttm pages.

Previously, dummy_read_page was used only for read-only user allocations; it
filled in pages that were not present in the user address map (presumably,
these were allocated but never written to pages).

This patch allows them to be used for read-only ttms allocated from the
kernel, so that applications can over-allocate buffers without forcing every
page to be allocated.

linux-core/drm_agpsupport.c

@@ -505,12 +505,14 @@ static int drm_agp_needs_unbind_cache_adjust(struct drm_ttm_backend *backend)
 
 
 static int drm_agp_populate(struct drm_ttm_backend *backend,
-			    unsigned long num_pages, struct page **pages)
+			    unsigned long num_pages, struct page **pages,
+			    struct page *dummy_read_page)
 {
 	struct drm_agp_ttm_backend *agp_be =
 		container_of(backend, struct drm_agp_ttm_backend, backend);
 	struct page **cur_page, **last_page = pages + num_pages;
 	DRM_AGP_MEM *mem;
+	int dummy_page_count = 0;
 
 	if (drm_alloc_memctl(num_pages * sizeof(void *)))
 		return -1;
@@ -528,8 +530,16 @@ static int drm_agp_populate(struct drm_ttm_backend *backend,
 
 	DRM_DEBUG("Current page count is %ld\n", (long) mem->page_count);
 	mem->page_count = 0;
-	for (cur_page = pages; cur_page < last_page; ++cur_page)
-		mem->memory[mem->page_count++] = phys_to_gart(page_to_phys(*cur_page));
+	for (cur_page = pages; cur_page < last_page; ++cur_page) {
+		struct page *page = *cur_page;
+		if (!page) {
+			page = dummy_read_page;
+			++dummy_page_count;
+		}
+		mem->memory[mem->page_count++] = phys_to_gart(page_to_phys(page));
+	}
+	if (dummy_page_count)
+		DRM_DEBUG("Mapped %d dummy pages\n", dummy_page_count);
 	agp_be->mem = mem;
 	return 0;
 }

linux-core/drm_objects.h

@@ -263,7 +263,8 @@ struct drm_ttm_backend;
 struct drm_ttm_backend_func {
 	int (*needs_ub_cache_adjust) (struct drm_ttm_backend *backend);
 	int (*populate) (struct drm_ttm_backend *backend,
-			 unsigned long num_pages, struct page **pages);
+			 unsigned long num_pages, struct page **pages,
+			 struct page *dummy_read_page);
 	void (*clear) (struct drm_ttm_backend *backend);
 	int (*bind) (struct drm_ttm_backend *backend,
 		     struct drm_bo_mem_reg *bo_mem);

linux-core/drm_ttm.c

@@ -262,7 +262,6 @@ int drm_ttm_set_user(struct drm_ttm *ttm,
 {
 	struct mm_struct *mm = tsk->mm;
 	int ret;
-	int i;
 	int write = (ttm->page_flags & DRM_TTM_PAGE_WRITE) != 0;
 
 	BUG_ON(num_pages != ttm->num_pages);
@@ -278,11 +277,6 @@ int drm_ttm_set_user(struct drm_ttm *ttm,
 		return -ENOMEM;
 	}
 
-	for (i = 0; i < num_pages; ++i) {
-		if (ttm->pages[i] == NULL)
-			ttm->pages[i] = ttm->dummy_read_page;
-	}
-
 	return 0;
 }
 
@@ -304,12 +298,14 @@ int drm_ttm_populate(struct drm_ttm *ttm)
 		return 0;
 
 	be = ttm->be;
+	if (ttm->page_flags & DRM_TTM_PAGE_WRITE) {
 		for (i = 0; i < ttm->num_pages; ++i) {
 			page = drm_ttm_get_page(ttm, i);
 			if (!page)
 				return -ENOMEM;
 		}
-	be->func->populate(be, ttm->num_pages, ttm->pages);
+	}
+	be->func->populate(be, ttm->num_pages, ttm->pages, ttm->dummy_read_page);
 	ttm->state = ttm_unbound;
 	return 0;
 }

linux-core/nouveau_sgdma.c

@@ -25,7 +25,7 @@ nouveau_sgdma_needs_ub_cache_adjust(struct drm_ttm_backend *be)
 
 static int
 nouveau_sgdma_populate(struct drm_ttm_backend *be, unsigned long num_pages,
-		       struct page **pages)
+		       struct page **pages, struct page *dummy_read_page)
 {
 	struct nouveau_sgdma_be *nvbe = (struct nouveau_sgdma_be *)be;
 	int p, d, o;
@@ -41,8 +41,11 @@ nouveau_sgdma_populate(struct drm_ttm_backend *be, unsigned long num_pages,
 	nvbe->pages_populated = d = 0;
 	for (p = 0; p < num_pages; p++) {
 		for (o = 0; o < PAGE_SIZE; o += NV_CTXDMA_PAGE_SIZE) {
+			struct page *page = pages[p];
+			if (!page)
+				page = dummy_read_page;
 			nvbe->pagelist[d] = pci_map_page(nvbe->dev->pdev,
-							 pages[p], o,
+							 page, o,
 							 NV_CTXDMA_PAGE_SIZE,
 							 PCI_DMA_BIDIRECTIONAL);
 			if (pci_dma_mapping_error(nvbe->pagelist[d])) {
@@ -299,7 +302,7 @@ nouveau_sgdma_nottm_hack_init(struct drm_device *dev)
 	}
 	dev_priv->gart_info.sg_handle = sgreq.handle;
 
-	if ((ret = be->func->populate(be, dev->sg->pages, dev->sg->pagelist))) {
+	if ((ret = be->func->populate(be, dev->sg->pages, dev->sg->pagelist, dev->bm.dummy_read_page))) {
 		DRM_ERROR("failed populate: %d\n", ret);
 		return ret;
 	}