From: Patrick Wildt <patrick@blueri.se>
Subject: Re: timecounting: start system uptime at 0.0, not 1.0
To: tech@openbsd.org
Cc: Scott Cheloha <scottcheloha@gmail.com>
Date: Mon, 19 Feb 2024 20:48:50 +0100

On Sun, Feb 18, 2024 at 06:25:19PM -0600, Scott Cheloha wrote:
> The system uptime starts at 1.0.  We inherited this from FreeBSD [1].
> My best guess is that something in FreeBSD depended (depends?) on the
> uptime being non-zero during boot.
> 
> patrick@ says this causes a problem in sdmmc(4).  In particular, the
> sdmmc_delay() call during sdmmc_enable() doesn't block the full 250ms.
> This is because the hardclock() starts at 0.0 and executes about hz
> times, rapidly, to "catch up" to 1.0.
> 
> Initializing th_offset to 0.0 fixes the problem: sdmmc_delay() blocks
> for the expected duration.
> 
> ok?

I can't judge why it's at 1.0 and not 0.0, but a tsleep() during HW init
not waiting for as long as we asked it to wait for... can wreak heavoc.

This works for me, ok patrick@ FWIW

> [1] http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/sys/kern/kern_tc.c?annotate=1.1
> 
>         !            76: static struct timehands th0 = {
>         !            77:        &dummy_timecounter,
>         !            78:        0,
>         !            79:        (uint64_t)-1 / 1000000,
>         !            80:        0,
> ->      !            81:        {1, 0},
>         !            82:        {0, 0},
>         !            83:        {0, 0},
>         !            84:        1,
>         !            85:        &th1
>         !            86: };
> 
> Index: kern_tc.c
> ===================================================================
> RCS file: /cvs/src/sys/kern/kern_tc.c,v
> diff -u -p -r1.82 kern_tc.c
> --- kern_tc.c	4 Feb 2023 19:19:36 -0000	1.82
> +++ kern_tc.c	18 Feb 2024 00:46:22 -0000
> @@ -96,7 +96,7 @@ static struct timehands th1 = {
>  static struct timehands th0 = {
>  	.th_counter = &dummy_timecounter,
>  	.th_scale = UINT64_MAX / 1000000,
> -	.th_offset = { .sec = 1, .frac = 0 },
> +	.th_offset = { .sec = 0, .frac = 0 },
>  	.th_generation = 1,
>  	.th_next = &th1
>  };
> @@ -117,7 +117,7 @@ static SLIST_HEAD(, timecounter) tc_list
>   * examining kernel core dumps.
>   */
>  volatile time_t naptime = 0;
> -volatile time_t time_second = 1;
> +volatile time_t time_second = 0;
>  volatile time_t time_uptime = 0;
>  
>  static int timestepwarnings;