drm/radeon: change vblank_time's calculation method to reduce computational error.

Ported from Rex's amdgpu change.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

diff --git a/drivers/gpu/drm/radeon/r600_dpm.c b/drivers/gpu/drm/radeon/r600_dpm.c
index 6a4b020..5a26eb4 100644 (file)
--- a/drivers/gpu/drm/radeon/r600_dpm.c
+++ b/drivers/gpu/drm/radeon/r600_dpm.c
@@ -156,19 +156,20 @@ u32 r600_dpm_get_vblank_time(struct radeon_device *rdev)
        struct drm_device *dev = rdev->ddev;
        struct drm_crtc *crtc;
        struct radeon_crtc *radeon_crtc;
-       u32 line_time_us, vblank_lines;
+       u32 vblank_in_pixels;
        u32 vblank_time_us = 0xffffffff; /* if the displays are off, vblank time is max */
 
        if (rdev->num_crtc && rdev->mode_info.mode_config_initialized) {
                list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
                        radeon_crtc = to_radeon_crtc(crtc);
                        if (crtc->enabled && radeon_crtc->enabled && radeon_crtc->hw_mode.clock) {
-                               line_time_us = (radeon_crtc->hw_mode.crtc_htotal * 1000) /
-                                       radeon_crtc->hw_mode.clock;
-                               vblank_lines = radeon_crtc->hw_mode.crtc_vblank_end -
-                                       radeon_crtc->hw_mode.crtc_vdisplay +
-                                       (radeon_crtc->v_border * 2);
-                               vblank_time_us = vblank_lines * line_time_us;
+                               vblank_in_pixels =
+                                       radeon_crtc->hw_mode.crtc_htotal *
+                                       (radeon_crtc->hw_mode.crtc_vblank_end -
+                                        radeon_crtc->hw_mode.crtc_vdisplay +
+                                        (radeon_crtc->v_border * 2));
+
+                               vblank_time_us = vblank_in_pixels * 1000 / radeon_crtc->hw_mode.clock;
                                break;
                        }
                }