RS232 consoles (was Re: NetBSD-7.0 boots OK and NetBSD-8.0 hangs/crashes during boot on a MacBook7,1)

["Aaron J. Grier" <agrier%poofygoof.com@localhost>]

(dropping current-users since this is more port-amd64 specific)

On Mon, Jul 06, 2020 at 10:07:37AM -0700, Steve Rikli wrote:
> I'd always hoped that, if anything, the "legacy" db9 connector might
> over time start turning into rj45 serial connectors with telco pinouts
> ala Cisco and other devices. But it doesn't seem a likely trend for PC
> systems at this point.

The reference server motherboards for Grantley (Haswell / Broadwell
Xeon) and the later Purley (Icelake / Cascade Lake) I've worked with
moved from DE9 to RJ45 for serial, so Intel-branded (and Intel OEM'd
systems) do have this.  I can't recall if it follows the cisco standard,
though.

> Even some of the recent name-brand "enterprise" rackmount systems at
> $work didn't come with a serial console port out the back -- it was an
> add-on option at most.  The vendors presumably want to push their GUI
> BMC paradigm, with the graphical server management goop. Some of it is
> admittedly nice functionality, but a lot of it is simply overkill when
> a good ole serial port would be fine.

IPMI defines serial-over-LAN which mostly works, and some BMCs implement
ssh to serial, which is better.  there's typically no need to touch the
GUI or a web interface at all, although resolution of the chicken-and-
egg configuration seems to be very vendor-specific.  (out-of-box boots OS over
PXE and configures BMC over IPMI/KCS?  out-of-box BMC does DHCP and
fetches initial configuration from returned DHCP parameters?  etc...)

Serial console redirection is definitely provided as part of the BIOS
reference code provided by Intel, although the IBVs seem to butcher
features as part of their "value-add" process.

> I think it's already been mentioned downthread, but other systems in
> this category are smaller devices like NUC and similar.  The low power
> (noise, heat etc.) profile makes those attractive, but without a
> serial console they're not as nice.  Best I've been able to do with a
> couple of those is a USB-serial terminal (!=console) which is better
> than nothing, e.g. to fix a broken network config, but doesn't help
> when you need to interact with boot stuff.

there seems to be a fundamental assumption on PC-based hardware (even
modern generation) that a VGA adapter is necessary to the point where
server BMCs implement a x4 PCIe endpoint for a VGA controller.  I've
been working for Intel for over a decade now and I still don't get it,
but maybe there are outside designs (facebook?) which omit this.

-- 
  Aaron J. Grier | "Not your ordinary poofy goof." | agrier%poofygoof.com@localhost
  "The price of reliability is the pursuit of the utmost simplicity.  It
   is a price which the very rich find most hard to pay."  -- Tony Hoare