[mm patch] i915: fix invalid opcode exception on cpus without clflush

[Kyle McMartin <kyle@mcmartin.ca>]

i915_flush_ttm was unconditionally executing a clflush instruction
to (obviously) flush the cache. Instead, check if the cpu supports
clflush, and if not, fall back to calling wbinvd to flush the entire
cache.

Signed-off-by: Kyle McMartin <kmcmartin@redhat.com>

--- a/drivers/char/drm/i915_buffer.c
+++ b/drivers/char/drm/i915_buffer.c
@@ -286,7 +286,18 @@ void i915_flush_ttm(struct drm_ttm *ttm)
 		return;
 
 	DRM_MEMORYBARRIER();
+
+#ifdef CONFIG_X86_32
+	/* Hopefully nobody has built an x86-64 processor without clflush */
+	if (!cpu_has_clflush) {
+		wbinvd();
+		DRM_MEMORYBARRIER();
+		return;
+	}
+#endif
+
 	for (i = ttm->num_pages - 1; i >= 0; i--)
 		drm_cache_flush_page(drm_ttm_get_page(ttm, i));
+
 	DRM_MEMORYBARRIER();
 }