Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC: r260889, r260890, r260911:

r260911 | imp | 2014-01-20 10:45:36 -0700 (Mon, 20 Jan 2014) | 5 lines

Don't lock in the generic grab just to lock again in the specific grabs.

r260890 | imp | 2014-01-19 12:39:13 -0700 (Sun, 19 Jan 2014) | 11 lines

Introduce grab and ungrab upcalls. When the kernel desires to grab the
console, it calls the grab functions. These functions should turn off
the RX interrupts, and any others that interfere. This makes mountroot
prompt work again. If there's more generalized need other than
prompting, many of these routines should be expanded to do those new
things.

Reviewed by: bde (with reservations)

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make the uart ns8250 high-level interface public rather than static.
This makes it easier to implement new drivers which are "mostly ns8250"
but with some small difference such as needing to enable clocks or poke
a non-standard register at probe or attach time.