In-progress (well... kind of) simple framebuffer support for visionfive2

[Jeff Rizzo <riz%tastylime.net@localhost>]

I've been fiddling with this for a week or two; since my attention is 
starting to wander, I wanted to get it in front of others before I 
completely lost interest.


With some changes to u-boot (which involve porting-forward the vendor 
driver to u-boot 2026.07) it becomes trivial to add genfb(4) to a kernel 
config, and get rudimentary video support on my visionfive 2 - the issue 
is that there's some cache issues that dirty the display every time 
there's a change until such time as the changes get flushed from the 
cache.  (I'm in the process of learning how that might be implemented, 
but I doubt even if I get something "working" it wouldn't be suitable 
for committing)


Anyway, if anyone else wanted to take a look, what's required is:


    - a replacement u-boot built from 
https://github.com/jeffrizzo/u-boot/tree/riz-starfive-visionfive2-video
      (built binaries available at 
https://www.netbsd.org/~riz/u-boot-visionfive2/ )

    - a kernel config like this:

include "arch/riscv/conf/GENERIC64"

genfb*          at fdt?                 # Simple Framebuffer
wsdisplay*      at wsemuldisplaydev?
options         WSEMUL_VT100
options         WSDISPLAY_CUSTOM_OUTPUT
options         WS_DEFAULT_FG=WSCOL_WHITE
options         WS_DEFAULT_BG=WSCOL_BLACK
options         WS_KERNEL_FG=WSCOL_GREEN
options         WS_KERNEL_BG=WSCOL_BLACK
options         WSDISPLAY_COMPAT_PCVT
options         WSDISPLAY_COMPAT_SYSCONS
options         WSDISPLAY_COMPAT_USL
options         WSDISPLAY_COMPAT_RAWKBD
options         WSDISPLAY_DEFAULTSCREENS=4
options         WSDISPLAY_MULTICONS
options         WSDISPLAY_SCROLLSUPPORT
pseudo-device   wsmux
pseudo-device   wsfont
options         FONT_BOLD8x16
options         FONT_BOLD16x32


... and possibly various wscons-related config changes if you want to 
try using it to log in - which you probably don't until the cache issues 
are resolved.


Anyway, I'll probably continue to mess around with this, but I'm not 
sure anything will ever come of it.  Anyone with suggestions for how to 
make it possible to map the fb with no cacheing, I'd love to hear them - 
I'm learning a bunch through this process, even if nothing ever hits the 
tree.


+j