drm/i915: Choose partial chunksize based on tile row size

In order to support setting up fences for partial mappings of an object,
we have to align those mappings with the fence. The minimum chunksize we
choose is at least the size of a single tile row.

v2: Make minimum chunk size a define for later use
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160818161718.27187-22-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -1669,6 +1669,16 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
 	return 0;
 }
 
+static unsigned int tile_row_pages(struct drm_i915_gem_object *obj)
+{
+	u64 size;
+
+	size = i915_gem_object_get_stride(obj);
+	size *= i915_gem_object_get_tiling(obj) == I915_TILING_Y ? 32 : 8;
+
+	return size >> PAGE_SHIFT;
+}
+
 /**
  * i915_gem_fault - fault a page into the GTT
  * @area: CPU VMA in question
@@ -1687,6 +1697,7 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
  */
 int i915_gem_fault(struct vm_area_struct *area, struct vm_fault *vmf)
 {
+#define MIN_CHUNK_PAGES ((1 << 20) >> PAGE_SHIFT) /* 1 MiB */
 	struct drm_i915_gem_object *obj = to_intel_bo(area->vm_private_data);
 	struct drm_device *dev = obj->base.dev;
 	struct drm_i915_private *dev_priv = to_i915(dev);
@@ -1728,7 +1739,11 @@ int i915_gem_fault(struct vm_area_struct *area, struct vm_fault *vmf)
 	/* Use a partial view if the object is bigger than the aperture. */
 	if (obj->base.size >= ggtt->mappable_end &&
 	    !i915_gem_object_is_tiled(obj)) {
-		static const unsigned int chunk_size = 256; // 1 MiB
+		unsigned int chunk_size;
+
+		chunk_size = MIN_CHUNK_PAGES;
+		if (i915_gem_object_is_tiled(obj))
+			chunk_size = max(chunk_size, tile_row_pages(obj));
 
 		memset(&view, 0, sizeof(view));
 		view.type = I915_GGTT_VIEW_PARTIAL;