8250 serial console conversion to NBCON queued again after earlier revert

The long-running effort to turn the 8250 serial driver into an NBCON console is back on track. John Ogness has posted a revised series that adds both threaded and atomic printing paths, and Greg Kroah-Hartman has queued it for the tty tree.

NBCON consoles let the kernel hand console ownership between contexts safely, including during panics, so emergency output is less likely to interleave or stall. The 8250 driver is one of the most common UART backends, so converting it matters for reliable serial consoles on a large share of systems.

An earlier version landed in the 6.14 merge window and was reverted before 6.14-rc1 after kernel test robot failures. Those turned out to be pre-existing 8250 issues rather than NBCON bugs; with the underlying problems fixed mainline, Ogness returned with a second attempt. The new work implements the required atomic and threaded write callbacks, performs hardware access inside unsafe sections, and supports per-byte handover with a preceding newline when one context takes over mid-line. Modem-control work that cannot run in atomic context is deferred via irq_work, with special handling around suspend and resume.

A follow-up patch restores a lockdep annotation that had been dropped while the driver still depended on oops_in_progress. Petr Mladek reviewed the series and discussed a small helper to reacquire ownership for post-write cleanup, which Ogness expects other NBCON drivers to need as more ports convert.