diff options
| -rw-r--r-- | src/common_drm.c | 19 |
1 files changed, 13 insertions, 6 deletions
diff --git a/src/common_drm.c b/src/common_drm.c index b5c7f0b..a3c017e 100644 --- a/src/common_drm.c +++ b/src/common_drm.c @@ -119,13 +119,20 @@ static uint64_t common_drm_frame_to_msc(xf86CrtcPtr crtc, uint32_t seq) { struct common_crtc_info *drmc = common_crtc(crtc); - if (seq < drmc->last_seq) { - if ((int32_t)(drmc->last_seq - seq) > 0x40000000) - drmc->last_msc += 0x100000000ULL; - else - seq = drmc->last_seq; - } + /* + * The sequence counter wrapped. Unlike the misleading comments in + * xf86-video-intel, the vblank counter is never wound backwards: it + * always runs forwards. However, since we don't monitor it with + * any regularity, it can appear to go backwards if we wait (eg) + * 0xc0000000 vblanks between calls. Hence, whenever we see the + * frame sequence less than the last sequence, assume that it has + * wrapped. (It may have wrapped more than once.) + */ + if (seq < drmc->last_seq) + drmc->last_msc += 0x100000000ULL; + drmc->last_seq = seq; + return drmc->last_msc + seq; } |