[PATCH] drm: Avoid the double clflush on the last cache line in drm_clflush_virt_range()

[Chris Wilson]

As the clflush operates on cache lines, and we can flush any byte
address, in order to flush all bytes given in the range we issue an
extra clflush on the last byte to ensure the last cacheline is flushed.
We can can the iteration to be over the actual cache lines to avoid this
double clflush on the last byte.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/drm_cache.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index 9a62d7a53553..6743ff7dccfa 100644
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c
@@ -130,11 +130,12 @@ drm_clflush_virt_range(void *addr, unsigned long length)
 {
 #if defined(CONFIG_X86)
 	if (cpu_has_clflush) {
+		const int size = boot_cpu_data.x86_clflush_size;
 		void *end = addr + length;
+		addr = (void *)(((unsigned long)addr) & -size);
 		mb();
-		for (; addr < end; addr += boot_cpu_data.x86_clflush_size)
+		for (; addr < end; addr += size)
 			clflushopt(addr);
-		clflushopt(end - 1);
 		mb();
 		return;
 	}
-- 
2.1.4