Re: [PATCH] Changes to support booting NetBSD/alpha

[Jason Thorpe]

> On Oct 6, 2020, at 9:42 PM, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
> 
> Hi Jason,
> 
> Well, this is not the correct way to do that, so this patch
> is unlikely to be accepted. We don't want Frankenstein models.
> 
> What is it you miss from the i82378? Why not implement the cy82c693ub?
> 
> The code you want to modify is in hw/alpha/dp264.c, see clipper_init().

The Clipper emulation *already* implements a Frankenstein model, a combination 
of hardware that DEC never shipped.  While some Tsunami-based systems did use 
the Cypress bridge, none of them, to my knowledge, had the CMD646 IDE 
controller.  The only system I'm aware of that shipped with a CMD646 IDE 
controller was the early version of the Miata (EV56 + Pyxis-based Digital 
Personal Workstation), and that system had the Intel i82378 PCI-ISA bridge.

The are a lot of differences in the Cypress PCI-ISA bridge, but most 
importantly, it has a different interrupt controller (the ELCR registers are 
programmed differently), and it has a different built-in IDE controller.  As 
far as I can tell, Qemu does not currently have emulation for the Cypress 
interrupt controller nor the Cypress IDE controller.

All Alpha systems that had a PCI-ISA bridge[*] shipped with, as far as I'm 
aware, one of 3 possible chips:

- Intel i82378 SIO
- Cypress 82C693
- Acer Labs M1533

...and the emulation provided by the existing Clipper model implements the 
Intel flavor (including the interrupt controller).  I just want software that 
expects one of those 3 chips to be there to work.  The existing emulation seems 
to assume that system software will just go out and probe the peripherals in 
the ISA space, but some operating systems (NetBSD in particular) support Alpha 
systems that have PCI without any ISA/LPC bus at all, and thus only go looking 
for ISA peripherals if a PCI-ISA bridge is present.  That is what my change 
here is intended to do, without changing any of the rest of the hardware 
configuration.


[*] ...ignoring the weirdo early models that had PCI + EISA + oddly-wired-up 
junk I/O chips.  Also, I don't have any direct experience with post-Titan 
models, so I'm not sure what they have...

-- thorpej