vt(4): Document kern.vt.fb.default_mode and kern.vt.fb.modes.*

Those tunables are used to set a specific mode in vt(4) instead of using
the default mode.

Differential Revision:	https://reviews.freebsd.org/D1098
Reviewed by:	ak@, emaste@, kwm@
MFC after:	1 week

1 files changed, 41 insertions, 1 deletions

diff --git a/share/man/man4/vt.4 b/share/man/man4/vt.4
index 351e559..ff3aadf 100644
--- a/share/man/man4/vt.4
+++ b/share/man/man4/vt.4
@@ -45,6 +45,8 @@ In
 .Xr loader.conf 5 :
 .Cd hw.vga.textmode=1
 .Cd kern.vty=vt
+.Cd kern.vt.fb.default_mode="<X>x<Y>"
+.Cd kern.vt.fb.modes.<connector>="<X>x<Y>"
 .Pp
 In
 .Xr loader.conf 5 or
@@ -176,7 +178,7 @@ Otherwise,
 switches to 640x480x16 VGA mode using
 .Cm vt_vga .
 If a KMS
-.Pq Kernel Mode Switching
+.Pq Kernel Mode Setting
 video driver is available, the display is switched to high resolution
 and the KMS driver takes over.
 When a KMS driver is not available,
@@ -203,6 +205,28 @@ By default,
 is used on computers that boot from BIOS, and
 .Nm
 is used on computers that boot from UEFI.
+.It Va kern.vt.fb.default_mode
+Set this value to a graphic mode to override the default mode picked by the
+.Nm
+backend. The mode is applied to all output connectors. This is currently
+only supported by the
+.Cm vt_fb
+backend when it's paired with a KMS video driver.
+.It Va kern.vt.fb.modes. Ns Pa connector_name
+Set this value to a graphic mode to override the default mode picked by the
+.Nm
+backend. This mode is applied to the output connector
+.Pa connector_name
+only. It has precedence over
+.Va kern.vt.fb.default_mode .
+To know the list of available connectors, load the KMS driver and look
+at
+.Xr dmesg 8 :
+it'll contain a list of connectors and their associated tunables. This
+is currently only supported by the
+.Cm vt_fb
+backend when it's paired with a KMS video driver.
+.El
 .Sh KEYBOARD SYSCTL TUNABLES
 These settings control whether certain special key combinations are enabled or
 ignored.
@@ -255,6 +279,22 @@ This line changes the default color of kernel messages to be bright red
 on a black background, or black on a bright red background when reversed.
 .Pp
 .Dl "options TERMINAL_KERN_ATTR=(FG_LIGHTRED|BG_BLACK)"
+.Pp
+To set a 1024x768 mode on all output connectors, put the following line in
+.Pa /boot/loader.conf :
+.Pp
+.Dl kern.vt.fb.default_mode="1024x768"
+.Pp
+To set a 800x600 only on a laptop builtin screen, use the following line instead:
+.Pp
+.Dl kern.vt.fb.modes.LVDS-1="800x600"
+.Pp
+The connector name was found in
+.Xr dmesg 8 :
+.Pp
+.Dl info: [drm] Connector LVDS-1: get mode from tunables:
+.Dl info: [drm]   - kern.vt.fb.modes.LVDS-1
+.Dl info: [drm]   - kern.vt.fb.default_mode
 .Sh SEE ALSO
 .Xr kbdcontrol 1 ,
 .Xr login 1 ,