All the following options belong to the DVI's Monitor section. To light two DVIs, add proper options to the DVI-2's Monitor section.

Basic Configuration

You may start from the basic options defined by Xorg.

Option       "Enable"                   "boolean"
Option       "Disable"                 "boolean"
Option       "Ignore"                    "boolean"
Option       "PreferredMode"    "string"
Option       "Position"                 "integer integer"
Option       "Rotate"                    "string"
Option       "LeftOf" ("RightOf", "Below", "Above")          "string"
Option       "MinClock"               "integer"
Option       "MaxClock"              "integer"

The following three options are exclusive, you can use only one or none. If none is set, X takes "enable" by default.

Option      "Enable"               "boolean" 
Option      "Disable"              "boolean" 
Option      "Ignore"                 "boolean"

Option "Enable" "boolean"

It means to light the DVI when starting X.

Option "Disable" "boolean"

It means not to light the DVI when starting X, but you could light it by the command "$ xrandr  --auto".

Option "Ignore" "boolean"

X will not create the output for the DVI. You could not light it dynamically by any means.

Option "PreferredMode" "string"

Set the display mode which would apply to DVI, say "1024x768". Note that if the DVI is disabled, you may not add this option. Otherwise, it could be lighted when X starts up.

Option "Position" "integer integer"

Set the start posotion of the output. The integers represents the position by two coordinates (x,y). The default value is "0 0". This option takes effect when two display devices are enabled. It makes no difference if only one is enabled.

Option "Rotate" "string"

Rotate the output of the DVI. The valid string could be left, right, normal, inverted, and the corresponding rotation degree is 270, 90, 0, 180 (CW). The default value is normal. To enable HW rotation, get more information from Chapter 6. Configuring Hardware rotation

Option "LeftOf"      "string"
Option "RightOf"    "string"
Option "Below"      "string"
Option "Above"      "string"

Enable the extend mode. If this option is not set when two display devices are enabled, the display mode would be clone mode. The string after the operator is one of the display device you intend to light. However, it's forbidden to use this option when only one display device is enabled.

Option "MinClock"    "integer"
Option "MaxClock"   "integer"

Put constrains to the display device, in order to filter out some mode. Unit: Hz.

DVI related options

Besides the options mentioned above, the VIA accelerated Linux graphics driver implemented other options to fulfill special requirements.

Option "Type" "string"

This option specifies in which way the DVI is connected to the board. Valid types are External, Internal. External means the DVI is connected via external transmitter, i.e. VT1632A. The default type is Internal.

Option "DIPort" "string"

This option specifies which digital port is occupied by the DVI. Valid ports are DFP_HIGH, DFP_LOW, DFP_HIGHLOW, DVP0, DVP1. The default value is determined by the display device and the Type setting. Usually, if Type is set to External, the default value is DVP1.

Option "SerialPort" "hex number"

This option is used to set the port to sense the external transmitter/encoder. The valid values are 0x25, 0x26, 0x2C, 0x31, 0x3D. If this option is not set, the VIA driver will sense the ports following this sequence: 0x2c-> 0x31-> 0x25-> 0x3D-> 0x26.

Option "DDCPort" "hex number"

This option is used to set the port to obtain EDID. The valid values are 0x25, 0x26, 0x2C, 0x31, 0x3D. The value is usually the same as SerialPort's. Thus, this option can not be set in most cases.

Option "NoDDCValue" "boolean"

This option is used when the display device's EDID is broken, but you strongly intend to light the device. It is not recommended to use, because the display device can be damaged. And when using this option, it's better to set modeline. Because in this case, device's modelist only includes the Xorg default modes, which are limited and may not have your desired mode.

Note that to avoid DI port conflicts, it's better to ignore the display devices which are not to be used.

You can get a complete sample in Appendix D. X Config Sample (Using the XRandR Extension).