xrandr：添加新模式

Question

我想使用 xrandr 添加新模式，但我有一个问题，xrandr 不想要！

~$ gtf 1280 1024 60

  # 1280x1024 @ 60.00 Hz (GTF) hsync: 63.60 kHz; pclk: 108.88 MHz
  Modeline "1280x1024_60.00"  108.88  1280 1360 1496 1712  1024 1025 1028 1060  -HSync +Vsync

~$ xrandr --newmode "1280x1024_60.00"  108.88  1280 1360 1496 1712  1024 1025 1028 1060  -HSync +Vsync
xrandr: Failed to get size of gamma for output default

我读了几个论坛，但没有办法。

我的 xorg.conf，也许它可以帮助：

Section "Device"
            Identifier      "fbturbo"
            #Identifier      "Allwinner A10/A13 FBDEV"
            Driver          "fbturbo"
            Option          "AccelMethod" "G2D"
            Option          "ShadowFB" "on"
            Option          "HWCursor" "true"
            Option          "DRI2" "true"
            Option          "DRI2HWOverlay" "true"
            Option          "fbdev" "/dev/fb0"
            Option          "SwapbuffersWait" "true"
            Option          "AccelMethod" "G2D"
    EndSection

    Section "Device"
            Identifier      "FBDEV 0"
            Driver          "fbturbo"
            Option          "fbdev" "/dev/fb0"
            Option          "AccelMethod" "G2D"
            Option          "ShadowFB" "on"
            Option          "HWCursor" "true"
            Option          "DRI2" "true"
            Option          "DRI2HWOverlay" "true"
            Option          "fbdev" "/dev/fb0"
            Option          "SwapbuffersWait" "true"
            Option          "AccelMethod" "G2D"
    EndSection

    Section "Device"
            Identifier      "FBDEV 1"
            Driver          "fbturbo"
            Option          "fbdev" "/dev/fb1"
            Option          "AccelMethod" "G2D"
            Option          "ShadowFB" "on"
            Option          "HWCursor" "true"
            Option          "DRI2" "true"
            Option          "DRI2HWOverlay" "true"
            Option          "fbdev" "/dev/fb0"
            Option          "SwapbuffersWait" "true"
            Option          "AccelMethod" "G2D"
    EndSection

    Section "Screen"
            Identifier      "_VGA_"
            Device          "FBDEV 0"
            Monitor         "VGA"
            DefaultDepth    24
            SubSection "Display"
                    Depth           24                  
                    Modes           "1280x1024"
            EndSubSection
    EndSection

    Section "Screen"
            Identifier      "_HDMI_"
            Device          "FBDEV 1"
            Monitor         "HDMI"
            DefaultDepth    24
            SubSection "Display"
                    Depth           24
                    Modes           "1440x900"
            EndSubSection
    EndSection

    Section "Monitor"
            Identifier      "VGA"
            Gamma           1.3
            Option          "PreferredMode" "1280x1024_60.00"
            Option          "DPMS" "true"
    EndSection

    Section "Monitor"
            Identifier      "HDMI"
            Gamma           1.3
            Option          "PreferredMode" "1440x900_60.00"
            Option          "Leftof" "VGA"
            Option          "DPMS" "true"
    EndSection

    Section "ServerLayout"
            Identifier      "Xinerama"
            Screen          0 "_VGA_"
            Screen          1 "_HDMI_" Leftof "_VGA_"
            Option      "Xinerama" "true"
            Option          "Clone" "false"
    EndSection

    Section "Extensions"
            Option "RANDR" "Enable"
            Option         "Composite" "Enable"
    EndSection

和

~$ xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1280 x 1024, current 1280 x 1024, maximum 1280 x 1024
default connected 1280x1024+0+0 0mm x 0mm
   1280x1024      60.0*

所以我的问题：如何设置输出默认伽玛？