Hi
We are fighting a rather strange issue with FPD lock loss with Qualcomm 8155P & DS90UB941AS-Q1. The DSI is in 4 lane continuous clock mode with LP transition of DSI data lanes once per frame (data lanes only, no LP on clock lane). Clock lane in high power and Non-burst VSync pulse modes.
Once in a while, mostly once or twice a minute but sometimes more often than that, there will be a brief FPD link loss for about ~100us or so followed by instant recovery. Visually it looks like a quick VSync tear but noticeable enough to be a major issue.
Now the strange part is that no errors get reported in either DSI or PHY error status registers on the 941AS. Also no DSI sync errors detected on any of the four lanes when it happens. The FPD CRC counter is also static / not rolling when the glitch happens.
What is even more puzzling is that we have two separate DSI outputs on this system driving a pair of 941AS -> 948 links with 2 identical 1920x1080@60 panels. The lock loss glitches will appear on both and are mostly synced between the two links! The lock loss will usually happen only 20-50us apart on the two separate FPD links.
No obvious DSI / FPD lane glitches or power anomalies we observed on the scope prior or during the FPD lock loss period. The BIST test is also succeeding just fine on both external DSI and internal OSC clocks.
Heres the relevant DSI config on the 8155P SoC:
psVideoModeConfg->eVideoTraffic = DSI_Video_TrafficMode_NonBurst_VSPulse;
psPowerOptions->bSendHsaHseAfterVsVe = FALSE;
psPowerOptions->bEnableLowPowerModeInHFP = FALSE;
psPowerOptions->bEnableLowPowerModeInHBP = FALSE;
psPowerOptions->bEnableLowPowerModeInHSA = FALSE;
psPowerOptions->bEnableLowPowerModeInBLLPEOF = TRUE;
psPowerOptions->bEnableLowPowerModeInBLLP = TRUE;
sDeviceConfig.bEnableClkLaneHighPwrMode = TRUE;
And this is what the DSI clock:
and DSI data:
look like.
I've been through (a rather brilliant) "DS90UB941AS-Q1 DSI Bringup Guide" by Casey McCrea and also some related threads on here like e.g.
but I'm still nowhere with this issue. Kind of running out of ideas what else to check.
Thanks for any pointers
