Re: [PATCH next v2 3/4] serial: 8250: Switch to nbcon console

John Ogness
2024-09-18T15:19:07Z

On 2024-09-18, Petr Mladek <pmladek@suse.com> wrote:
> It would be fair to mention that it does not longer support fifo in
> the 8250 driver. It basically reverted the commit 8f3631f0f6eb42e5
> ("serial/8250: Use fifo in 8250 console driver").

Agreed.

> It is not usable in write_thread() because it would not allow
> a safe takeover between emitting particular characters.

If write_thread could exit_unsafe()/enter_unsafe() while busy-waiting,
then emergency/panic could still take over at any time. Even if it means
that atomic_write() would need to first wait for the FIFO to drain
(which it will). The important thing is that emergency/panic is able to
take over.

I dropped the optimization to keep things simple for now, but I agree
with Andy that it would be unfortunate. I will take a look at what such
an implementation could look like.

John