Enabling DMA
I tried enabling DMA by patching the DTSI as was done in 5.15. It seems to be working.
The dma files in /sys/class still read 0. Can you confirm this on your device?
Observations
The CPU usage has reduced considerably, almost to the levels of that seen with USB. Thank you!
However, I have observed spikes of up to 50% almost every 5 seconds. Do you know of anything that could cause this?
“Spikes” are observed with the USB method (experiment 2) as well, but only to about 5%. These “spikes” have the same pattern as that with UART+DMA.