1 files changed, 37 insertions, 23 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 9ac73dd1b422..dc2e6fdb6ca3 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -171,6 +171,37 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
         return 0;
 }
 
+/*
+ * Try to write quickly with an atomic kmap. Return true on success.
+ *
+ * If this fails (which includes a partial write), we'll redo the whole
+ * thing with the slow version.
+ *
+ * This is a workaround for the low performance of iounmap (approximate
+ * 10% cpu cost on normal 3D workloads).  kmap_atomic on HIGHMEM kernels
+ * happens to let us map card memory without taking IPIs.  When the vmap
+ * rework lands we should be able to dump this hack.
+ */
+static inline int fast_user_write(unsigned long pfn, char __user *user_data,
+                                  int l, int o)
+{
+#ifdef CONFIG_HIGHMEM
+        unsigned long unwritten;
+        char *vaddr_atomic;
+
+        vaddr_atomic = kmap_atomic_pfn(pfn, KM_USER0);
+#if WATCH_PWRITE
+        DRM_INFO("pwrite i %d o %d l %d pfn %ld vaddr %p\n",
+                 i, o, l, pfn, vaddr_atomic);
+#endif
+        unwritten = __copy_from_user_inatomic_nocache(vaddr_atomic + o, user_data, l);
+        kunmap_atomic(vaddr_atomic, KM_USER0);
+        return !unwritten;
+#else
+        return 0;
+#endif
+}
+
 static int
 i915_gem_gtt_pwrite(struct drm_device *dev, struct drm_gem_object *obj,
                     struct drm_i915_gem_pwrite *args,
@@ -180,12 +211,7 @@ i915_gem_gtt_pwrite(struct drm_device *dev, struct drm_gem_object *obj,
         ssize_t remain;
         loff_t offset;
         char __user *user_data;
-        char __iomem *vaddr;
-        char *vaddr_atomic;
-        int i, o, l;
         int ret = 0;
-        unsigned long pfn;
-        unsigned long unwritten;
 
         user_data = (char __user *) (uintptr_t) args->data_ptr;
         remain = args->size;
@@ -209,6 +235,9 @@ i915_gem_gtt_pwrite(struct drm_device *dev, struct drm_gem_object *obj,
         obj_priv->dirty = 1;
 
         while (remain > 0) {
+                unsigned long pfn;
+                int i, o, l;
+
                 /* Operation in this page
                  *
                  * i = page number
@@ -223,25 +252,10 @@ i915_gem_gtt_pwrite(struct drm_device *dev, struct drm_gem_object *obj,
 
                 pfn = (dev->agp->base >> PAGE_SHIFT) + i;
 
-#ifdef CONFIG_HIGHMEM
-                /* This is a workaround for the low performance of iounmap
-                 * (approximate 10% cpu cost on normal 3D workloads).
-                 * kmap_atomic on HIGHMEM kernels happens to let us map card
-                 * memory without taking IPIs.  When the vmap rework lands
-                 * we should be able to dump this hack.
-                 */
-                vaddr_atomic = kmap_atomic_pfn(pfn, KM_USER0);
-#if WATCH_PWRITE
-                DRM_INFO("pwrite i %d o %d l %d pfn %ld vaddr %p\n",
-                         i, o, l, pfn, vaddr_atomic);
-#endif
-                unwritten = __copy_from_user_inatomic_nocache(vaddr_atomic + o,
-                                                              user_data, l);
-                kunmap_atomic(vaddr_atomic, KM_USER0);
+                if (!fast_user_write(pfn, user_data, l, o)) {
+                        unsigned long unwritten;
+                        char __iomem *vaddr;
 
-                if (unwritten)
-#endif /* CONFIG_HIGHMEM */
-                {
                         vaddr = ioremap_wc(pfn << PAGE_SHIFT, PAGE_SIZE);
 #if WATCH_PWRITE
                         DRM_INFO("pwrite slow i %d o %d l %d "