On 06.09.24 3:46 AM, Adam Ford wrote: > I have been testing various settings on the HDMI out of the i.MX8MP. > > I noticed that sometimes my monitor would not sync, but sometimes it > would on the same resolution/refresh rate. Frieder noted the LCDIF > was sometimes underflowing, so read up on it a little bit. > > In the comments of the LCDIF driver, it's noted: > Set FIFO Panic watermarks, low 1/3, high 2/3 . > > However, in the downstream kernels, NXP changes the threshold to 1/2 > and 3/4 on the LCDIF that drives the HDMI, while leaving the other > LCDIF interfaces at the default. > > When I increased the threshold to 1/2 and 3/4, it appeared that > several resolutions that my monitor was struggling to sync started > working, and it appeared to sync faster. I don't have an HDMI > analyzer, so I cannot verify much beyond knowing if my monitor can or > cannot sync. For me this change doesn't seem to cause any improved behavior. My monitor still fails to sync every few times I run "modetest -s" . Also we have a downstream kernel based on 6.1 with backported HDMI support and I don't see the issues there. But I need to make some further tests to make any reliable statements. > > Could the threshold and underrun cause this monitor intermittent > issue, or would this be something else? > > Does it make sense to have a flag or device tree option to override > the default thresholds to change the panic level? > > adam
