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Add new kern.vt.slow_down tunable.
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Browse Source 
On a laptop with no other console devices than the screen, things
scroll of the screen faster than eye or camera can capture it.

This tunable slows the console down and makes it update synchronously,
so console output continues when timers or interrupts do not.

Differential Revision:  https://reviews.freebsd.org/D47710
This commit is contained in:
Poul-Henning Kamp 2024-11-23 15:01:09 +00:00
parent e012d79c9c
commit 7749de2440
2 changed files with 20 additions and 0 deletions
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11
share/man/man4/vt.4
View File

@ -50,6 +50,7 @@ In
.Cd kern.vt.color.<colornum>.rgb="<colorspec>"
.Cd kern.vt.fb.default_mode="<X>x<Y>"
.Cd kern.vt.fb.modes.<connector>="<X>x<Y>"
.Cd kern.vt.slow_down=<delay>"
.Cd screen.font="<X>x<Y>"
.Pp
In
@ -266,6 +267,16 @@ It will contain a list of connectors and their associated tunables.
This is currently only supported by the
.Cm vt_fb
backend when it is paired with a KMS video driver.
.It Va kern.vt.slow_down
When debugging the kernel on modern laptops, the screen is often
the only available console, and relevant information will scroll
out of view before it can be captured by eye or camera.
.Pp
Setting
.Va kern.vt.slow_down
to a non-zero number will make console output synchronous (ie:
not dependent on timers and interrupts) and slow it down in proportion
to the number.
.It Va screen.font
Set this value to the base name of the desired font file located in
.Pa /boot/fonts .

9
sys/dev/vt/vt_core.c
View File

@ -132,6 +132,9 @@ static VT_SYSCTL_INT(debug, 0, "vt(9) debug level");
static VT_SYSCTL_INT(deadtimer, 15, "Time to wait busy process in VT_PROCESS mode");
static VT_SYSCTL_INT(suspendswitch, 1, "Switch to VT0 before suspend");
/* Slow down and dont rely on timers and interrupts */
static VT_SYSCTL_INT(slow_down, 0, "Non-zero make console slower and synchronous.");
/* Allow to disable some keyboard combinations. */
static VT_SYSCTL_INT(kbd_halt, 1, "Enable halt keyboard combination. "
"See kbdmap(5) to configure.");
@ -1657,6 +1660,12 @@ vtterm_done(struct terminal *tm)
}
vd->vd_flags &= ~VDF_SPLASH;
vt_flush(vd);
} else if (vt_slow_down > 0) {
int i, j;
for (i = 0; i < vt_slow_down; i++) {
for (j = 0; j < 1000; j++)
vt_flush(vd);
}
} else if (!(vd->vd_flags & VDF_ASYNC)) {
vt_flush(vd);
}