Documentation/fb/uvesafb.txt

   1
   2 uvesafb - A Generic Driver for VBE2+ compliant video cards
   3 ==========================================================
   4
   5 1. Requirements
   6 ---------------
   7
   8 uvesafb should work with any video card that has a Video BIOS compliant
   9 with the VBE 2.0 standard.
  10
  11 Unlike other drivers, uvesafb makes use of a userspace helper called
  12 v86d.  v86d is used to run the x86 Video BIOS code in a simulated and
  13 controlled environment.  This allows uvesafb to function on arches other
  14 than x86.  Check the v86d documentation for a list of currently supported
  15 arches.
  16
  17 v86d source code can be downloaded from the following website:
  18   http://dev.gentoo.org/~spock/projects/uvesafb
  19
  20 Please refer to the v86d documentation for detailed configuration and
  21 installation instructions.
  22
  23 Note that the v86d userspace helper has to be available at all times in
  24 order for uvesafb to work properly.  If you want to use uvesafb during
  25 early boot, you will have to include v86d into an initramfs image, and
  26 either compile it into the kernel or use it as an initrd.
  27
  28 2. Caveats and limitations
  29 --------------------------
  30
  31 uvesafb is a _generic_ driver which supports a wide variety of video
  32 cards, but which is ultimately limited by the Video BIOS interface.
  33 The most important limitations are:
  34
  35 - Lack of any type of acceleration.
  36 - A strict and limited set of supported video modes.  Often the native
  37   or most optimal resolution/refresh rate for your setup will not work
  38   with uvesafb, simply because the Video BIOS doesn't support the
  39   video mode you want to use.  This can be especially painful with
  40   widescreen panels, where native video modes don't have the 4:3 aspect
  41   ratio, which is what most BIOS-es are limited to.
  42 - Adjusting the refresh rate is only possible with a VBE 3.0 compliant
  43   Video BIOS.  Note that many nVidia Video BIOS-es claim to be VBE 3.0
  44   compliant, while they simply ignore any refresh rate settings.
  45
  46 3. Configuration
  47 ----------------
  48
  49 uvesafb can be compiled either as a module, or directly into the kernel.
  50 In both cases it supports the same set of configuration options, which
  51 are either given on the kernel command line or as module parameters, e.g.:
  52
  53  video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel)
  54
  55  # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap  (module)
  56
  57 Accepted options:
  58
  59 ypan    Enable display panning using the VESA protected mode
  60         interface.  The visible screen is just a window of the
  61         video memory, console scrolling is done by changing the
  62         start of the window.  Available on x86 only.
  63
  64 ywrap   Same as ypan, but assumes your gfx board can wrap-around
  65         the video memory (i.e. starts reading from top if it
  66         reaches the end of video memory).  Faster than ypan.
  67         Available on x86 only.
  68
  69 redraw  Scroll by redrawing the affected part of the screen, this
  70         is the safe (and slow) default.
  71
  72 (If you're using uvesafb as a module, the above three options are
  73  used a parameter of the scroll option, e.g. scroll=ypan.)
  74
  75 vgapal  Use the standard VGA registers for palette changes.
  76
  77 pmipal  Use the protected mode interface for palette changes.
  78         This is the default if the protected mode interface is
  79         available.  Available on x86 only.
  80
  81 mtrr:n  Setup memory type range registers for the framebuffer
  82         where n:
  83               0 - disabled (equivalent to nomtrr) (default)
  84               1 - uncachable
  85               2 - write-back
  86               3 - write-combining
  87               4 - write-through
  88
  89         If you see the following in dmesg, choose the type that matches
  90         the old one.  In this example, use "mtrr:2".
  91 ...
  92 mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
  93 ...
  94
  95 nomtrr  Do not use memory type range registers.
  96
  97 vremap:n
  98         Remap 'n' MiB of video RAM.  If 0 or not specified, remap memory
  99         according to video mode.
 100
 101 vtotal:n
 102         If the video BIOS of your card incorrectly determines the total
 103         amount of video RAM, use this option to override the BIOS (in MiB).
 104
 105 <mode>  The mode you want to set, in the standard modedb format.  Refer to
 106         modedb.txt for a detailed description.  When uvesafb is compiled as
 107         a module, the mode string should be provided as a value of the
 108         'mode_option' option.
 109
 110 vbemode:x
 111         Force the use of VBE mode x.  The mode will only be set if it's
 112         found in the VBE-provided list of supported modes.
 113         NOTE: The mode number 'x' should be specified in VESA mode number
 114         notation, not the Linux kernel one (eg. 257 instead of 769).
 115         HINT: If you use this option because normal <mode> parameter does
 116         not work for you and you use a X server, you'll probably want to
 117         set the 'nocrtc' option to ensure that the video mode is properly
 118         restored after console <-> X switches.
 119
 120 nocrtc  Do not use CRTC timings while setting the video mode.  This option
 121         has any effect only if the Video BIOS is VBE 3.0 compliant.  Use it
 122         if you have problems with modes set the standard way.  Note that
 123         using this option implies that any refresh rate adjustments will
 124         be ignored and the refresh rate will stay at your BIOS default (60 Hz).
 125
 126 noedid  Do not try to fetch and use EDID-provided modes.
 127
 128 noblank Disable hardware blanking.
 129
 130 v86d:path
 131         Set path to the v86d executable. This option is only available as
 132         a module parameter, and not as a part of the video= string.  If you
 133         need to use it and have uvesafb built into the kernel, use
 134         uvesafb.v86d="path".
 135
 136 Additionally, the following parameters may be provided.  They all override the
 137 EDID-provided values and BIOS defaults.  Refer to your monitor's specs to get
 138 the correct values for maxhf, maxvf and maxclk for your hardware.
 139
 140 maxhf:n     Maximum horizontal frequency (in kHz).
 141 maxvf:n     Maximum vertical frequency (in Hz).
 142 maxclk:n    Maximum pixel clock (in MHz).
 143
 144 4. The sysfs interface
 145 ----------------------
 146
 147 uvesafb provides several sysfs nodes for configurable parameters and
 148 additional information.
 149
 150 Driver attributes:
 151
 152 /sys/bus/platform/drivers/uvesafb
 153   - v86d (default: /sbin/v86d)
 154     Path to the v86d executable. v86d is started by uvesafb
 155     if an instance of the daemon isn't already running.
 156
 157 Device attributes:
 158
 159 /sys/bus/platform/drivers/uvesafb/uvesafb.0
 160   - nocrtc
 161     Use the default refresh rate (60 Hz) if set to 1.
 162
 163   - oem_product_name
 164   - oem_product_rev
 165   - oem_string
 166   - oem_vendor
 167     Information about the card and its maker.
 168
 169   - vbe_modes
 170     A list of video modes supported by the Video BIOS along with their
 171     VBE mode numbers in hex.
 172
 173   - vbe_version
 174     A BCD value indicating the implemented VBE standard.
 175
 176 5. Miscellaneous
 177 ----------------
 178
 179 Uvesafb will set a video mode with the default refresh rate and timings
 180 from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
 181
 182
 183 --
 184  Michal Januszewski <spock@gentoo.org>
 185  Last updated: 2007-06-16
 186
 187  Documentation of the uvesafb options is loosely based on vesafb.txt.
 188