I recently ported my https://github.com/juj/fbcp-ili9341/ driver over to also work on ILI9486 as well.
Check out a demo video at https://www.youtube.com/watch?v=dqOLIHOjLq4
My result was that the maximum I am able to drive a WaveShare 3.5" (B) display is 31.875MHz SPI bus speed, achieved by setting core_freq=255, and choosing a SPI Clock Divider of 8, i.e. 255/8=31.875MHz. A speed of core_freq=256 and CDIV=8, i.e. 256/8=32.00MHz was too much and the display starts to show garbled colors.
I'm now curious about the manufacturing variances that exist on the different ILI9486 displays. I wonder if each display reaches close to identical SPI bus speeds, or if there are even large variances between these to be expected.
If someone has a ILI9486 or a ILI9486L display and has the curiosity to try out https://github.com/juj/fbcp-ili9341/ on it, I'd be interested to hear how fast you are able to tune your display to run at with fbcp-ili9341? That is, which core_freq+CDIV combos work out for you, and which ones did not?
Especially negative results are interesting, since they tell the most about the particular speed limits of a copy.
(This is just for recreative hacking against the SPI constraints, I don't have a particular use case in mind)
Thanks for any data you might be able to share, much appreciated!