drm: add helper to clflush a virtual address range

Useful when the page is already mapped to copy date in/out.

For -stable because the next patch (fixing phys obj pwrite) needs this
little helper function.
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_cache.c

@@ -98,3 +98,26 @@ drm_clflush_pages(struct page *pages[], unsigned long num_pages)
 #endif
 }
 EXPORT_SYMBOL(drm_clflush_pages);
+
+void
+drm_clflush_virt_range(char *addr, unsigned long length)
+{
+#if defined(CONFIG_X86)
+	if (cpu_has_clflush) {
+		char *end = addr + length;
+		mb();
+		for (; addr < end; addr += boot_cpu_data.x86_clflush_size)
+			clflush(addr);
+		clflush(end - 1);
+		mb();
+		return;
+	}
+
+	if (on_each_cpu(drm_clflush_ipi_handler, NULL, 1) != 0)
+		printk(KERN_ERR "Timed out waiting for cache flush.\n");
+#else
+	printk(KERN_ERR "Architecture has no drm_cache.c support\n");
+	WARN_ON_ONCE(1);
+#endif
+}
+EXPORT_SYMBOL(drm_clflush_virt_range);

include/drm/drmP.h

@@ -1332,6 +1332,7 @@ extern int drm_remove_magic(struct drm_master *master, drm_magic_t magic);
 
 /* Cache management (drm_cache.c) */
 void drm_clflush_pages(struct page *pages[], unsigned long num_pages);
+void drm_clflush_virt_range(char *addr, unsigned long length);
 
 				/* Locking IOCTL support (drm_lock.h) */
 extern int drm_lock(struct drm_device *dev, void *data,