Re: [coreboot] PIC instead of APIC mode for KolibriOS - mouse fix

[Scott Duplichan]

ron minnich [mailto:[e-mail]] wrote:

]So, how would these changes affect other payloads?
]
]ron

The patch adds programming and one reporting
mechanism for PIC mode PCI interrupt routing for
the ASRock E350M1 board only. Without the patch,
PIC mode PCI interrupt routing is not programmed
and not reported. There are several ways an OS can
find PIC mode interrupt routing for PCI devices:
1) $PIR table
2) ACPI
3) PCI config space interrupt line registers
This change adds reporting method 3. Reporting
methods 1 and 2 are incomplete or unimplemented
for this board.

This patch programs PIC mode PCI interrupt routing
to match the OEM BIOS. Without the patch, PIC mode
PCI interrupt routing is unprogrammed. The changes
affect an OS or other code that uses PCI interrupts
in PIC mode. APIC mode is unaffected.
> From what I can remember, older mainstream operating

systems normally use the ACPI method to find PIC mode
interrupt routing. They might fall back to $PIR or 
even the config space line register method I suppose.
I see some coreboot boards support the ACPI method of
reporting (and modifying) PIC mode PCI interrupts.
However I don't see this this code in E350M1 project.
As a result, an OS such as Windows 2000 may or may not
see improvement with this patch. I didn't try it. Linux
still supports PIC mode PCI interrupt routing through
grub options. I did not test that either. It seems
interest in PIC mode interrupts has waned since
multicore processors have become popular. A limitation
of PIC mode interrupts is that all PCI interrupts are
handled by the BSP core and cannot be routed to AP cores.

I know of one application that uses PIC mode PCI 
interrupts and finds them from the config space line
register. It is the interrupt test portion of the
Broadcom b57diag utility.

For operating systems, Windows dropped PIC mode starting
with XP x64 edition if I remember correctly. XP 32-bit
defaults to APIC mode, but can be switched to PIC mode
during installation. After XP, all PIC mode is gone.
For linux, PIC mode is still supported, but the default
was switched to APIC mode several years ago. I believe 
there was a time with 32-bit Linux used PIC mode but
64-bit used APIC mode. This is from memory so I could
be a little off.

Thanks,
Scott

PIC instead of APIC mode for KolibriOS - mouse fix

[ron minnich]

Thanks, that's a great explanation. Generally, we've tried to avoid
too much hardware setup in coreboot; that's the job of the kernel. I'm
not really happy that we're doing all this PIC setup for one OS,
written in assembly. It's been quite some time since I've had to use
PIC mode at all.

Why can't the Kolibrios just use modern standards? And why all this
effort for an OS written in assembly anyway?

Unix v6 kernels were the same size as Kolibrios. They were written in
C. That was 40 years ago. It's bizarre, to say the least, to be
booting a kernel written in assembly from firmware written in C.

Hence, I find it hard to believe that we want this patch. But I'm
wrong a lot, so if I am here too, just let me know.

ron