EDID stands for Extended Display Identification Data. It is a data structure provided by a computer display to describe its capabilities to a graphics card. It is what enables a modern personal computer to know what kind of monitor is connected. EDID is defined by the Video Electronics Standards Association (VESA). The EDID includes manufacturer name, product type, phosphor or filter type, timings supported by the display, display size, luminance data and (for digital displays only) pixel mapping data.

The channel for transmitting the EDID from the display to the graphics card is usually the I²C bus. The combination of EDID and I²C is called the Display Data Channel (DDC). Before DDC and EDID were defined, there was no standard way for a graphics card to know what kind of display device it was connected to.

To light the single display device by EDID, the following per-conditions should be satisfied at the same time.

• xorg > 7.0

• The display devide (computer display) has its EDID.

Currently, most display devices, including CRT, LCD panel, DVI, HDMI have EDID. Regarding to those display devices without EDID, the VIA driver will light them by the built-in timing.

• Not using the user-specified modeline in the X config file.

For the VIA accelerated Linux graphics driver, the modeline settings have the first piority when lighting the display devices. Get more information about modeline settings from Part III. Chapter 7. Modeline Support.

• If set the mode in Section "Screen", this mode should be defined in the display device's EDID. So if you are not clear about the Detailed Timing Descriptors (DTD) table in the display device's EDID, it 's recommendded not to set the preferred mode.

For example,

Section "Screen"
       Monitor  "Monitor"
       SubSection "Display"
              Modes  "1024x768" 
              Depth  24
       EndSubSection
       DefaultDepth 24
       Device       "Device[0]"
       Identifier   "Screen[0]"
EndSection

In Section "Screen", the preferred mode is set to be 1024x768, if this mode is defined in the display device's EDID, the VIA driver will light the display device by its EDID. Otherwise, the VIA driver will light it by the built-in timing.

In the Duo-view display mode, the VIA driver only supports the primary display device's EDID, and light the secondary by the built-in timing. The first one appears in Option "ActiveDevie" "string1, string2" is the primary.

In the SAMM display mode, there are two independent Screen sections, so both devices can use their own EDID.

However, if you do not want to light the display device by its EDID, you can add the option below to Section "Device" to disable it. In this case, the driver will light the device in a mandatory way.

Option "NoDDCValue"

It is not recommended to use this option. The display device can be damaged if the given mode is beyond its ablility.