drm/ttm: fix caching problem on non-PAT systems.

http://bugzilla.kernel.org/show_bug.cgi?id=15328

This fixes a serious regression on AGP/non-PAT systems, where
pages were ending up in the wrong state and slowing down the
whole system.

[airlied: taken this from the bug as the other option is to revert
the change which caused it].

Tested-by: John W. Linville (in bug).
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 11 insertions, 7 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index e2123af7775a..3d47a2c12322 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -196,14 +196,15 @@ EXPORT_SYMBOL(ttm_tt_populate);
 
 #ifdef CONFIG_X86
 static inline int ttm_tt_set_page_caching(struct page *p,
-                                          enum ttm_caching_state c_state)
+                                          enum ttm_caching_state c_old,
+                                          enum ttm_caching_state c_new)
 {
         int ret = 0;
 
         if (PageHighMem(p))
                 return 0;
 
-        if (get_page_memtype(p) != -1) {
+        if (c_old != tt_cached) {
                 /* p isn't in the default caching state, set it to
                  * writeback first to free its current memtype. */
 
@@ -212,16 +213,17 @@ static inline int ttm_tt_set_page_caching(struct page *p,
                         return ret;
         }
 
-        if (c_state == tt_wc)
+        if (c_new == tt_wc)
                 ret = set_memory_wc((unsigned long) page_address(p), 1);
-        else if (c_state == tt_uncached)
+        else if (c_new == tt_uncached)
                 ret = set_pages_uc(p, 1);
 
         return ret;
 }
 #else /* CONFIG_X86 */
 static inline int ttm_tt_set_page_caching(struct page *p,
-                                          enum ttm_caching_state c_state)
+                                          enum ttm_caching_state c_old,
+                                          enum ttm_caching_state c_new)
 {
         return 0;
 }
@@ -254,7 +256,9 @@ static int ttm_tt_set_caching(struct ttm_tt *ttm,
         for (i = 0; i < ttm->num_pages; ++i) {
                 cur_page = ttm->pages[i];
                 if (likely(cur_page != NULL)) {
-                        ret = ttm_tt_set_page_caching(cur_page, c_state);
+                        ret = ttm_tt_set_page_caching(cur_page,
+                                                      ttm->caching_state,
+                                                      c_state);
                         if (unlikely(ret != 0))
                                 goto out_err;
                 }
@@ -268,7 +272,7 @@ out_err:
         for (j = 0; j < i; ++j) {
                 cur_page = ttm->pages[j];
                 if (likely(cur_page != NULL)) {
-                        (void)ttm_tt_set_page_caching(cur_page,
+                        (void)ttm_tt_set_page_caching(cur_page, c_state,
                                                       ttm->caching_state);
                 }
         }