[PATCH 03/24] drm/i915: Pin backing pages for pwrite

[Chris Wilson <chris@chris-wilson.co.uk>]

By using the recently introduced pinning of pages, we can safely drop
the mutex in the knowledge that the pages are not going to disappear
beneath us, and so we can simplify the code for iterating over the pages.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c |   37 +++++++++++++------------------------
 1 file changed, 13 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 98c434c7..f1a0fc7 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -690,7 +690,7 @@ shmem_pwrite_fast(struct page *page, int shmem_page_offset, int page_length,
 				       page_length);
 	kunmap_atomic(vaddr);
 
-	return ret;
+	return ret ? -EFAULT : 0;
 }
 
 /* Only difference to the fast-path function is that this can handle bit17
@@ -724,7 +724,7 @@ shmem_pwrite_slow(struct page *page, int shmem_page_offset, int page_length,
 					     page_do_bit17_swizzling);
 	kunmap(page);
 
-	return ret;
+	return ret ? -EFAULT : 0;
 }
 
 static int
@@ -733,7 +733,6 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
 		      struct drm_i915_gem_pwrite *args,
 		      struct drm_file *file)
 {
-	struct address_space *mapping = obj->base.filp->f_path.dentry->d_inode->i_mapping;
 	ssize_t remain;
 	loff_t offset;
 	char __user *user_data;
@@ -742,7 +741,6 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
 	int hit_slowpath = 0;
 	int needs_clflush_after = 0;
 	int needs_clflush_before = 0;
-	int release_page;
 
 	user_data = (char __user *) (uintptr_t) args->data_ptr;
 	remain = args->size;
@@ -768,6 +766,12 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
 	    && obj->cache_level == I915_CACHE_NONE)
 		needs_clflush_before = 1;
 
+	ret = i915_gem_object_get_pages(obj);
+	if (ret)
+		return ret;
+
+	i915_gem_object_pin_pages(obj);
+
 	offset = args->offset;
 	obj->dirty = 1;
 
@@ -793,18 +797,7 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
 			((shmem_page_offset | page_length)
 				& (boot_cpu_data.x86_clflush_size - 1));
 
-		if (obj->pages) {
-			page = obj->pages[offset >> PAGE_SHIFT];
-			release_page = 0;
-		} else {
-			page = shmem_read_mapping_page(mapping, offset >> PAGE_SHIFT);
-			if (IS_ERR(page)) {
-				ret = PTR_ERR(page);
-				goto out;
-			}
-			release_page = 1;
-		}
-
+		page = obj->pages[offset >> PAGE_SHIFT];
 		page_do_bit17_swizzling = obj_do_bit17_swizzling &&
 			(page_to_phys(page) & (1 << 17)) != 0;
 
@@ -816,26 +809,20 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
 			goto next_page;
 
 		hit_slowpath = 1;
-		page_cache_get(page);
 		mutex_unlock(&dev->struct_mutex);
-
 		ret = shmem_pwrite_slow(page, shmem_page_offset, page_length,
 					user_data, page_do_bit17_swizzling,
 					partial_cacheline_write,
 					needs_clflush_after);
 
 		mutex_lock(&dev->struct_mutex);
-		page_cache_release(page);
+
 next_page:
 		set_page_dirty(page);
 		mark_page_accessed(page);
-		if (release_page)
-			page_cache_release(page);
 
-		if (ret) {
-			ret = -EFAULT;
+		if (ret)
 			goto out;
-		}
 
 		remain -= page_length;
 		user_data += page_length;
@@ -843,6 +830,8 @@ next_page:
 	}
 
 out:
+	i915_gem_object_unpin_pages(obj);
+
 	if (hit_slowpath) {
 		/* Fixup: Kill any reinstated backing storage pages */
 		if (obj->madv == __I915_MADV_PURGED)
-- 
1.7.10.4