I915

i915 is a kernel module:

a xorg.conf could look something like this:

       Section "Device"
       Option     "DRI"                "true" # [<bool>]
       Option     "ColorKey"                  #      
       Option     "VideoKey"                  # 
       Option     "AccelMethod"         "SNA"
       Option     "FallbackDebug"       "false"      # [<bool>]
       Option     "Tiling"             "true"        # [<bool>]
       Option     "LinearFramebuffer"  "true"       # [<bool>]  
       Option     "Shadow"             "false"        # [<bool>]
       Option     "SwapbuffersWait"    "false"        # [<bool>]
       Option     "TripleBuffer"       "false"       # [<bool>] 
       Option     "XvMC"                      # [<bool>]       
       Option     "XvPreferOverlay"           # [<bool>]
       Option     "DebugFlushBatches" "false"         # [<bool>]
       Option     "DebugFlushCaches"   "false"        # [<bool>]
       Option     "DebugWait"          "false"        # [<bool>]
       Option     "HotPlug"            "true"       # [<bool>] 
       Option     "RelaxedFencing"     "false"        # [<bool>]
       Option     "BufferCache"        "true" # [<bool>]        
       Option "Throttle" "false"
       Identifier  "Card0" 
       Driver      "intel"   
       BusID       "PCI:0:2:0"
       EndSection

also ~/.drirc must be this:

   <driconf>
        <device screen="0" driver="dri2">
        <application name="Default">
        <option name="vblank_mode" value="0" />
       </application>
     </device>
    </driconf>

or this:

    <driconf>
   <device screen="0" driver="dri2">
       <application name="Default">
           <option name="vblank_mode" value="0" />
       </application>
   </device>
   <device screen="0" driver="i915">
       <application name="Default">
           <option name="force_s3tc_enable" value="true" />
           <option name="no_rast" value="false" />
           <option name="always_flush_cache" value="false" />
           <option name="stub_occlusion_query" value="false" />
           <option name="shader_precompile" value="false" />
           <option name="hiz" value="false" />
           <option name="always_flush_batch" value="false" />
           <option name="bo_reuse" value="0" />
           <option name="early_z" value="true" />
           <option name="force_glsl_extensions_warn" value="false" />
           <option name="disable_glsl_line_continuations" value="false" />
           <option name="texture_tiling" value="false" />
           <option name="disable_blend_func_extended" value="false" />
           <option name="vblank_mode" value="0" />
           <option name="allow_large_textures" value="0" />
           <option name="fragment_shader" value="false" />
       </application>
   </device>
   </driconf>