Re: [RFC PATCH v2] hw/display/tcx: Allow 64-bit accesses to framebuffer stippler and blitter

[Michael <macallan@netbsd.org>]

Hello,

On Sat, 29 Aug 2020 18:45:06 +0200
Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:

> > > > However the NetBSD revision 1.32 of the driver introduced
> > > > 64-bit accesses to the stippler and blitter [2]. It is safe
> > > > to assume these memory regions are 64-bit accessible.
> > > > QEMU implementation is 32-bit, so fill the 'impl' fields.  
> >
> > IIRC the real hardware *requires* 64bit accesses for stipple and
> > blitter operations to work. For stipples you write a 64bit word into
> > STIP space, the address defines where in the framebuffer you want to
> > draw, the data contain a 32bit bitmask, foreground colour and a ROP.
> > BLIT space works similarly, the 64bit word contains an offset were to
> > read pixels from, and how many you want to copy.
> >  
> 
> Thanks Michael for this information!
> If you don't mind I'll amend it to the commit description so there is a
> reference for posterity.

One more thing since there seems to be some confusion - 64bit accesses
on the framebuffer are fine as well. TCX/S24 is *not* an SBus device,
even though its node says it is.
S24 is a card that plugs into a special slot on the SS5 mainboard,
which is shared with an SBus slot and looks a lot like a horizontal UPA
slot. Both S24 and TCX are accessed through the Micro/TurboSPARC's AFX
bus which is 64bit wide and intended for graphics.
Early FFB docs even mentioned connecting to both AFX and UPA, no idea
if that was ever realized in hardware though.

have fun
Michael