I hadn’t noticed that - that’s the GPU device, not the DSI channel, but that would explain why it’s failing when it tries to get the MIPI host device. Maybe down to devicetree changes from 5.10 to 5.15 breaking the overlay? Let me try a couple things…
Also, worth noting that panel-ili9881c.c supports the ili9881d as well, as of late last year - but the controller isn’t hooked directly to the Pi’s i2c bus, so some custom-ness is needed regardless. To be honest I’m not entirely sure exactly what the driver is trying and failing to do here, so not really sure where to look. I’m sure seeed will have it figured out soon enough 