[PATCH] drm/amd/display: Fix psr static frames calculation

[Harry Wentland]

From: Roman Li <Roman.Li at amd.com>

[Why]
Driver crash with psr feature enabled due to divide-by-zero error.
This is a regression after rework to calculate static screen frame
number entry time.

[How]
Correct order of operations to avoid divide-by-zero.

Cc: Colin Ian King <colin.king at canonical.com>
Fixes: 5b5abe952607 drm/amd/display: make PSR static screen entry within 30 ms
Cc: stable at vger.kernel.org
Signed-off-by: Roman Li <roman.li at amd.com>
Reviewed-by: Zhan Liu <Zhan.Liu at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index eed3ed7180fd..61c36c1520c2 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -8491,7 +8491,6 @@ bool amdgpu_dm_psr_enable(struct dc_stream_state *stream)
 	/* Calculate number of static frames before generating interrupt to
 	 * enter PSR.
 	 */
-	unsigned int frame_time_microsec = 1000000 / vsync_rate_hz;
 	// Init fail safe of 2 frames static
 	unsigned int num_frames_static = 2;
 
@@ -8506,8 +8505,10 @@ bool amdgpu_dm_psr_enable(struct dc_stream_state *stream)
 	 * Calculate number of frames such that at least 30 ms of time has
 	 * passed.
 	 */
-	if (vsync_rate_hz != 0)
+	if (vsync_rate_hz != 0) {
+		unsigned int frame_time_microsec = 1000000 / vsync_rate_hz;
 		num_frames_static = (30000 / frame_time_microsec) + 1;
+	}
 
 	params.triggers.cursor_update = true;
 	params.triggers.overlay_update = true;
-- 
2.25.0