If the displays are off, set the vblank time to max to make
sure mclk switching is enabled.  Avoid mclk getting set
to high when no displays are attached.

bug: https://bugs.freedesktop.org/show_bug.cgi?id=101528
fixes: 09be4a5219 (drm/amd/powerplay/smu7: add vblank check for mclk switching (v2))
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c
index c6dba1e..8b8eda7 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c

@@ -838,6 +838,9 @@ static int amdgpu_cgs_get_active_displays_info(struct cgs_device *cgs_device,
 		return -EINVAL;
 
 	mode_info = info->mode_info;
+	if (mode_info)
+		/* if the displays are off, vblank time is max */
+		mode_info->vblank_time_us = 0xffffffff;
 
 	if (adev->mode_info.num_crtc && adev->mode_info.mode_config_initialized) {
 		list_for_each_entry(crtc,