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.Dd May 30, 2017
.Dt VGA_SWITCHEROO 4
.Os
.Sh NAME
.Nm vga_switcheroo ,
.Nm apple_gmux
.Nd support for Apple laptops with dual GPUs
.Sh SYNOPSIS
To enable support of dual GPUs in kernel, include the following
line in the kernel configuration file:
.Bd -ragged -offset indent
.Cd "options VGA_SWITCHEROO"
.Ed
.Pp
When the system has booted, load the apple_gmux
driver before the native graphics drivers, for example
.Xr i915 4 .
.Pp
Alternatively, you can put these two lines in
.Xr rc.conf 5 :
.Bd -literal -offset indent
apple_gmux_load="YES"
i915_load="YES"
.Ed
.Pp
As a result, vga_switcheroo switches the gmux controller so that all
output comes from the IGD.
.Sh DESCRIPTION
Apple MacBook Pro laptops have hybrid graphics, i.e.\& two GPUs, one being
the integrated graphics device (IGD) and the other being the discrete
graphics device (DIS), sometimes called the dedicated graphics device.
Gmux is a microcontroller that controls the output of these GPUs.
.Pp
.Nm vga_switcheroo
is the higher level module that facilitates switching between the two
GPUs using the lower level
.Nm apple_gmux
driver.
When the system boots and
.Nm vga_switcheroo
is enabled,
.Nm apple_gmux
registers with it.
It then acts as a handler.
The two graphics adapters will also detect the presence of
.Nm vga_switcheroo
and register as clients.
.Sh IMPLEMENTATION NOTES
In the current
.Dx
specific implementation, upon detecting the presence of
.Nm apple_gmux ,
the Intel driver will call
.Nm
to switch the gmux so that all output comes from the IGD.
Switching to DIS is not yet supported.
.Sh HARDWARE
Apple MacBook Pro laptops with dual GPUs.
.Sh SEE ALSO
.Xr i915 4 ,
.Xr rc.conf 5
.Pp
.Pa https://01.org/linuxgraphics/gfx-docs/drm/gpu/vga-switcheroo.html
.Sh HISTORY
The
.Nm
driver was added in
.Dx 4.9 .
.Sh AUTHORS
The
.Nm
driver was ported to
.Dx
from linux 4.8 by
.An Peeter Must .
He also wrote this manual page.