[PATCH RESEND] drm/ttm: expose CPU address of DMA-allocated pages

[Alexandre Courbot]

Pages allocated using the DMA API have a coherent memory mapping. Make
this mapping visible to drivers so they can decide to use it instead of
creating their own redundant one.

This is not a mere optimization: for instance, on ARM it is illegal to
have several memory mappings to the same memory with different protection.
The mapping provided by dma_alloc_coherent() and exposed by this patch is
guaranteed to be safe, but subsequent mappings performed by drivers are
not. Thus drivers using the DMA page allocator should use this mapping
instead of creating their own.

Signed-off-by: Alexandre Courbot <acourbot at nvidia.com>
---
This patch was previously part of a series but I figured it would make more
sense to send it separately. It is to be used by Nouveau (and hopefully
other drivers) on ARM.

 drivers/gpu/drm/ttm/ttm_page_alloc_dma.c | 2 ++
 drivers/gpu/drm/ttm/ttm_tt.c             | 6 +++++-
 include/drm/ttm/ttm_bo_driver.h          | 2 ++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
index fb8259f69839..0301fac5badd 100644
--- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
+++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
@@ -847,6 +847,7 @@ static int ttm_dma_pool_get_pages(struct dma_pool *pool,
 	if (count) {
 		d_page = list_first_entry(&pool->free_list, struct dma_page, page_list);
 		ttm->pages[index] = d_page->p;
+		ttm_dma->cpu_address[index] = d_page->vaddr;
 		ttm_dma->dma_address[index] = d_page->dma;
 		list_move_tail(&d_page->page_list, &ttm_dma->pages_list);
 		r = 0;
@@ -978,6 +979,7 @@ void ttm_dma_unpopulate(struct ttm_dma_tt *ttm_dma, struct device *dev)
 	INIT_LIST_HEAD(&ttm_dma->pages_list);
 	for (i = 0; i < ttm->num_pages; i++) {
 		ttm->pages[i] = NULL;
+		ttm_dma->cpu_address[i] = 0;
 		ttm_dma->dma_address[i] = 0;
 	}
 
diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index 75f319090043..341594ede596 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -58,6 +58,8 @@ static void ttm_dma_tt_alloc_page_directory(struct ttm_dma_tt *ttm)
 	ttm->ttm.pages = drm_calloc_large(ttm->ttm.num_pages, sizeof(void*));
 	ttm->dma_address = drm_calloc_large(ttm->ttm.num_pages,
 					    sizeof(*ttm->dma_address));
+	ttm->cpu_address = drm_calloc_large(ttm->ttm.num_pages,
+					    sizeof(*ttm->cpu_address));
 }
 
 #ifdef CONFIG_X86
@@ -228,7 +230,7 @@ int ttm_dma_tt_init(struct ttm_dma_tt *ttm_dma, struct ttm_bo_device *bdev,
 
 	INIT_LIST_HEAD(&ttm_dma->pages_list);
 	ttm_dma_tt_alloc_page_directory(ttm_dma);
-	if (!ttm->pages || !ttm_dma->dma_address) {
+	if (!ttm->pages || !ttm_dma->dma_address || !ttm_dma->cpu_address) {
 		ttm_tt_destroy(ttm);
 		pr_err("Failed allocating page table\n");
 		return -ENOMEM;
@@ -243,6 +245,8 @@ void ttm_dma_tt_fini(struct ttm_dma_tt *ttm_dma)
 
 	drm_free_large(ttm->pages);
 	ttm->pages = NULL;
+	drm_free_large(ttm_dma->cpu_address);
+	ttm_dma->cpu_address = NULL;
 	drm_free_large(ttm_dma->dma_address);
 	ttm_dma->dma_address = NULL;
 }
diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
index 202f0a7171e8..1d9f0f1ff52d 100644
--- a/include/drm/ttm/ttm_bo_driver.h
+++ b/include/drm/ttm/ttm_bo_driver.h
@@ -133,6 +133,7 @@ struct ttm_tt {
  * struct ttm_dma_tt
  *
  * @ttm: Base ttm_tt struct.
+ * @cpu_address: The CPU address of the pages
  * @dma_address: The DMA (bus) addresses of the pages
  * @pages_list: used by some page allocation backend
  *
@@ -142,6 +143,7 @@ struct ttm_tt {
  */
 struct ttm_dma_tt {
 	struct ttm_tt ttm;
+	void **cpu_address;
 	dma_addr_t *dma_address;
 	struct list_head pages_list;
 };
-- 
2.0.1