drm/i915: add support for 64K scratch page

Before we can fully enable 64K pages, we need to first support a 64K
scratch page if we intend to support the case where we have object sizes
< 2M, since any scratch PTE must also point to a 64K region.  Without
this our 64K usage is limited to objects which completely fill the
page-table, and therefore don't need any scratch.

v2: add reminder about why 48b PPGTT

Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006145041.21673-14-matthew.auld@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006221833.32439-13-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 79ba485..7eae6ab 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -519,22 +519,63 @@ static void fill_page_dma_32(struct i915_address_space *vm,
 static int
 setup_scratch_page(struct i915_address_space *vm, gfp_t gfp)
 {
-       struct page *page;
+       struct page *page = NULL;
        dma_addr_t addr;
+       int order;
 
-       page = alloc_page(gfp | __GFP_ZERO);
-       if (unlikely(!page))
-               return -ENOMEM;
+       /*
+        * In order to utilize 64K pages for an object with a size < 2M, we will
+        * need to support a 64K scratch page, given that every 16th entry for a
+        * page-table operating in 64K mode must point to a properly aligned 64K
+        * region, including any PTEs which happen to point to scratch.
+        *
+        * This is only relevant for the 48b PPGTT where we support
+        * huge-gtt-pages, see also i915_vma_insert().
+        *
+        * TODO: we should really consider write-protecting the scratch-page and
+        * sharing between ppgtt
+        */
+       if (i915_vm_is_48bit(vm) &&
+           HAS_PAGE_SIZES(vm->i915, I915_GTT_PAGE_SIZE_64K)) {
+               order = get_order(I915_GTT_PAGE_SIZE_64K);
+               page = alloc_pages(gfp | __GFP_ZERO, order);
+               if (page) {
+                       addr = dma_map_page(vm->dma, page, 0,
+                                           I915_GTT_PAGE_SIZE_64K,
+                                           PCI_DMA_BIDIRECTIONAL);
+                       if (unlikely(dma_mapping_error(vm->dma, addr))) {
+                               __free_pages(page, order);
+                               page = NULL;
+                       }
 
-       addr = dma_map_page(vm->dma, page, 0, PAGE_SIZE,
-                           PCI_DMA_BIDIRECTIONAL);
-       if (unlikely(dma_mapping_error(vm->dma, addr))) {
-               __free_page(page);
-               return -ENOMEM;
+                       if (!IS_ALIGNED(addr, I915_GTT_PAGE_SIZE_64K)) {
+                               dma_unmap_page(vm->dma, addr,
+                                              I915_GTT_PAGE_SIZE_64K,
+                                              PCI_DMA_BIDIRECTIONAL);
+                               __free_pages(page, order);
+                               page = NULL;
+                       }
+               }
+       }
+
+       if (!page) {
+               order = 0;
+               page = alloc_page(gfp | __GFP_ZERO);
+               if (unlikely(!page))
+                       return -ENOMEM;
+
+               addr = dma_map_page(vm->dma, page, 0, PAGE_SIZE,
+                                   PCI_DMA_BIDIRECTIONAL);
+               if (unlikely(dma_mapping_error(vm->dma, addr))) {
+                       __free_page(page);
+                       return -ENOMEM;
+               }
        }
 
        vm->scratch_page.page = page;
        vm->scratch_page.daddr = addr;
+       vm->scratch_page.order = order;
+
        return 0;
 }
 
@@ -542,8 +583,9 @@ static void cleanup_scratch_page(struct i915_address_space *vm)
 {
        struct i915_page_dma *p = &vm->scratch_page;
 
-       dma_unmap_page(vm->dma, p->daddr, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
-       __free_page(p->page);
+       dma_unmap_page(vm->dma, p->daddr, BIT(p->order) << PAGE_SHIFT,
+                      PCI_DMA_BIDIRECTIONAL);
+       __free_pages(p->page, p->order);
 }
 
 static struct i915_page_table *alloc_pt(struct i915_address_space *vm)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
index b9d7036..e9de3f0 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_gtt.h
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
@@ -215,6 +215,7 @@ struct i915_vma;
 
 struct i915_page_dma {
        struct page *page;
+       int order;
        union {
                dma_addr_t daddr;