On Wed, Feb 05, 2025 at 09:34:21AM -0800, Jason Thorpe wrote:
> > On Feb 4, 2025, at 11:40 PM, Simon Burge <sim...@netbsd.org> wrote:
> > Emile `iMil' Heitor wrote:
> > --- a/sys/dev/ic/com.c
> > +++ b/sys/dev/ic/com.c
> > @@ -589,8 +589,15 @@ com_attach_subr(struct com_softc *sc)
> > break;
> > }
> >
> > + if (!inside_vm_guest()) {
> > + /*
> > + * Wait for output to finish. No need for
> > + * a delay on virtual machines.
> > + */
> > + delay(10000);
>
> As for the com(4)-specific bit: why are we inserting a blanket
> 10ms delay *at all*? If we’re concerned about garbling
> output-in-progress on real hardware, isn’t there some register we
> can look at, or something?
That is a good question. That delay was already present when cgd@ checked
in rev 1.1. With no good explanation.
LSR bits 5 (THRE) and 6 (TSRE/TEMT) have been available since the original
INS8250 for checking if the transmitter is completely empty.
Why it didn't loop on those bits is anyone's guess.
--chris
