HVSI serial console review (2.6 patch)

[Hollis Blanchard]

Attached is the diff I'm planning on sending upstream soon for the Host
Virtual Serial Interface, a firmware feature that few have had the
pleasure of using yet.

It changes drivers/char/hvc_console.c a little bit; renaming the
arch-provided functions and altering that interface somewhat. I'm a
little uncertain about the tty_hangup() call; I may need to make it look
more like uart_handle_dcd_change(). Nobody should notice any normal
(Regatta/JS20) console difference other than an extra function pointer
dereference.

The bulk of the code is is arch/ppc64/kernel/hvconsole.c. It's an
elaborate protocol that allows us to get read/write/ioctl out of a
read/write hcall interface. It has seen some testing, and for the most
part "works for me". Comments here are welcome too: areas of criticism
could range from adding 1KiB to BSS size to overly-complicated buffering
to "this is an awful design" (I'll sympathise with the last, but can't
change it). If anyone actually cares, I'd be happy to describe the
workings in a little more detail. I meant to give an overview of HVSI in
the code but forgot, so I'll have to add that in later.

--
Hollis Blanchard
IBM Linux Technology Center
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