On Fri, Sep 01, 2017 at 04:07:16PM +0900, Hoegeun Kwon wrote:
If scanout started, we should reduce etime by delta_ns. But delta_ns is negative if scanout has not started. If delta_ns is negative, subtraction of delta_ns from etime increases etime. This is wrong, the etime should not be increased, so you have to make delta_ns an absolute value.
Signed-off-by: Hoegeun Kwon hoegeun.kwon@samsung.com
Hello all,
I think that the etime should not be increased. In cases where delta_ns is negative, if you get time again after an interrupt call, there is a problem that the time obtained from the interrupt becomes the future time instead of the past time.
Please let me know if this patch is wrong.
It is wrong. The timestamp corresponds to the first active pixel of the frame/field. So while between vblank start and active start we expect to get a timestamp that is in the future.
Best regards, Hoegeun
drivers/gpu/drm/drm_vblank.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c index 70f2b95..a3e0176 100644 --- a/drivers/gpu/drm/drm_vblank.c +++ b/drivers/gpu/drm/drm_vblank.c @@ -684,7 +684,7 @@ bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev, /* Subtract time delta from raw timestamp to get final * vblank_time timestamp for end of vblank. */
- etime = ktime_sub_ns(etime, delta_ns);
etime = ktime_sub_ns(etime, abs(delta_ns)); *vblank_time = ktime_to_timeval(etime);
DRM_DEBUG_VBL("crtc %u : v p(%d,%d)@ %ld.%ld -> %ld.%ld [e %d us, %d rep]\n",
-- 1.9.1
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