[PATCH 3.16 127/306] drm/radeon: change vblank_time's calculation method to reduce computational error.

Ben Hutchings
2017-02-16T00:08:55Z

From: Alex Deucher <alexander.deucher@amd.com>

commit 02cfb5fccb0f9f968f0e208d89d9769aa16267bc upstream.

Ported from Rex's amdgpu change.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/gpu/drm/radeon/r600_dpm.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

--- a/drivers/gpu/drm/radeon/r600_dpm.c
+++ b/drivers/gpu/drm/radeon/r600_dpm.c
@@ -155,19 +155,20 @@ u32 r600_dpm_get_vblank_time(struct rade
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;
}
}