Re: kern/55286: Kernel messages cause loss of serial console input

[Martin Husemann <martin%duskware.de@localhost>]

The following reply was made to PR kern/55286; it has been noted by GNATS.

From: Martin Husemann <martin%duskware.de@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/55286: Kernel messages cause loss of serial console input
Date: Mon, 25 May 2020 14:56:07 +0200

 Here is a patch that uses readahead in comcnputc only while we are still
 cold - compile tested only, but should fix the problem as well.
 
 
 Martin
 
 Index: com.c
 ===================================================================
 RCS file: /cvsroot/src/sys/dev/ic/com.c,v
 retrieving revision 1.358
 diff -u -p -r1.358 com.c
 --- com.c	1 May 2020 07:27:51 -0000	1.358
 +++ com.c	25 May 2020 12:48:20 -0000
 @@ -159,7 +159,7 @@ int	com_to_tiocm(struct com_softc *);
  void	com_iflush(struct com_softc *);
  
  int	com_common_getc(dev_t, struct com_regs *);
 -static void	com_common_putc(dev_t, struct com_regs *, int);
 +static void	com_common_putc(dev_t, struct com_regs *, int, int);
  
  int	cominit(struct com_regs *, int, int, int, tcflag_t);
  
 @@ -2399,12 +2399,12 @@ com_common_getc(dev_t dev, struct com_re
  }
  
  static void
 -com_common_putc(dev_t dev, struct com_regs *regsp, int c)
 +com_common_putc(dev_t dev, struct com_regs *regsp, int c, int with_readahead)
  {
  	int s = splserial();
  	int cin, stat, timo;
  
 -	if (com_readaheadcount < MAX_READAHEAD
 +	if (with_readahead && com_readaheadcount < MAX_READAHEAD
  	     && ISSET(stat = CSR_READ_1(regsp, COM_REG_LSR), LSR_RXRDY)) {
  		int cn_trapped = 0;
  		cin = CSR_READ_1(regsp, COM_REG_RXDATA);
 @@ -2572,7 +2572,7 @@ void
  comcnputc(dev_t dev, int c)
  {
  
 -	com_common_putc(dev, &comcons_info.regs, c);
 +	com_common_putc(dev, &comcons_info.regs, c, cold);
  }
  
  void
 @@ -2641,7 +2641,7 @@ void
  com_kgdb_putc(void *arg, int c)
  {
  
 -	com_common_putc(NODEV, &comkgdbregs, c);
 +	com_common_putc(NODEV, &comkgdbregs, c, 0);
  }
  #endif /* KGDB */