Possible fix for DEC 2000 / Jensen

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

Nigel Johnson wrote on port-alpha@:

> I have a DEC2000 AXP model 300 that I would love to get NetBSD on, but
> right now
> it comes up with a bad memory SIMM.

Off topic, but this reminds me an old todo item.

In NetBSD 4.0 days, DEC2000 / Jensen support was still incomplete
and it hung right after interrupts were enabled:
 https://mail-index.netbsd.org/netbsd-bugs/2007/07/22/0001.html
 https://gnats.netbsd.org/36628

Recently Miod Vallat told me that he found a Jensen's quirk
in a Linux source and suggested a possible fix for NetBSD/alpha.

I was so lazy to call for testers for the suggested change,
but finally I've committed it (Jensen has never worked anyway):

https://mail-index.netbsd.org/source-changes/2020/09/19/msg122103.html
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Modified Files:
	src/sys/arch/alpha/jensenio: com_jensenio.c

Log Message:
Possible fix for hangup on Jensen mentioned in PR/36628.

According to comments in Linux drivers/tty/serial/8250/8250.h,
 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/tty/serial/8250/8250.h?h=v5.8#n242
the driver has to set OUT1 and OUT2 lines for "some ALPHA"
otherwise "the machine locks up with endless interrupts."
Note OUT2 (MCR_IENABLE) is set in MI com_attach_subr()
so we have to set OUT1 (MCR_DSR) in the MD attachment.

The information was notified from Miod Vallat.
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If anyone still has a working Jensen, it's much appreciated to test
a current daily snapshot kernel (or 9.0 with the above change)
on it.

Thanks,

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Izumi Tsutsui