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.  This option is available on x86
  63         only and is the default option on that architecture.
  64
  65 ywrap   Same as ypan, but assumes your gfx board can wrap-around
  66         the video memory (i.e. starts reading from top if it
  67         reaches the end of video memory).  Faster than ypan.
  68         Available on x86 only.
  69
  70 redraw  Scroll by redrawing the affected part of the screen, this
  71         is the default on non-x86.
  72
  73 (If you're using uvesafb as a module, the above three options are
  74  used a parameter of the scroll option, e.g. scroll=ypan.)
  75
  76 vgapal  Use the standard VGA registers for palette changes.
  77
  78 pmipal  Use the protected mode interface for palette changes.
  79         This is the default if the protected mode interface is
  80         available.  Available on x86 only.
  81
  82 mtrr:n  Setup memory type range registers for the framebuffer
  83         where n:
  84               0 - disabled (equivalent to nomtrr) (default)
  85               1 - uncachable
  86               2 - write-back
  87               3 - write-combining
  88               4 - write-through
  89
  90         If you see the following in dmesg, choose the type that matches
  91         the old one.  In this example, use "mtrr:2".
  92 ...
  93 mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
  94 ...
  95
  96 nomtrr  Do not use memory type range registers.
  97
  98 vremap:n
  99         Remap 'n' MiB of video RAM.  If 0 or not specified, remap memory
 100         according to video mode.
 101
 102 vtotal:n
 103         If the video BIOS of your card incorrectly determines the total
 104         amount of video RAM, use this option to override the BIOS (in MiB).
 105
 106 <mode>  The mode you want to set, in the standard modedb format.  Refer to
 107         modedb.txt for a detailed description.  When uvesafb is compiled as
 108         a module, the mode string should be provided as a value of the
 109         'mode_option' option.
 110
 111 vbemode:x
 112         Force the use of VBE mode x.  The mode will only be set if it's
 113         found in the VBE-provided list of supported modes.
 114         NOTE: The mode number 'x' should be specified in VESA mode number
 115         notation, not the Linux kernel one (eg. 257 instead of 769).
 116         HINT: If you use this option because normal <mode> parameter does
 117         not work for you and you use a X server, you'll probably want to
 118         set the 'nocrtc' option to ensure that the video mode is properly
 119         restored after console <-> X switches.
 120
 121 nocrtc  Do not use CRTC timings while setting the video mode.  This option
 122         has any effect only if the Video BIOS is VBE 3.0 compliant.  Use it
 123         if you have problems with modes set the standard way.  Note that
 124         using this option implies that any refresh rate adjustments will
 125         be ignored and the refresh rate will stay at your BIOS default (60 Hz).
 126
 127 noedid  Do not try to fetch and use EDID-provided modes.
 128
 129 noblank Disable hardware blanking.
 130
 131 v86d:path
 132         Set path to the v86d executable. This option is only available as
 133         a module parameter, and not as a part of the video= string.  If you
 134         need to use it and have uvesafb built into the kernel, use
 135         uvesafb.v86d="path".
 136
 137 Additionally, the following parameters may be provided.  They all override the
 138 EDID-provided values and BIOS defaults.  Refer to your monitor's specs to get
 139 the correct values for maxhf, maxvf and maxclk for your hardware.
 140
 141 maxhf:n     Maximum horizontal frequency (in kHz).
 142 maxvf:n     Maximum vertical frequency (in Hz).
 143 maxclk:n    Maximum pixel clock (in MHz).
 144
 145 4. The sysfs interface
 146 ----------------------
 147
 148 uvesafb provides several sysfs nodes for configurable parameters and
 149 additional information.
 150
 151 Driver attributes:
 152
 153 /sys/bus/platform/drivers/uvesafb
 154   - v86d (default: /sbin/v86d)
 155     Path to the v86d executable. v86d is started by uvesafb
 156     if an instance of the daemon isn't already running.
 157
 158 Device attributes:
 159
 160 /sys/bus/platform/drivers/uvesafb/uvesafb.0
 161   - nocrtc
 162     Use the default refresh rate (60 Hz) if set to 1.
 163
 164   - oem_product_name
 165   - oem_product_rev
 166   - oem_string
 167   - oem_vendor
 168     Information about the card and its maker.
 169
 170   - vbe_modes
 171     A list of video modes supported by the Video BIOS along with their
 172     VBE mode numbers in hex.
 173
 174   - vbe_version
 175     A BCD value indicating the implemented VBE standard.
 176
 177 5. Miscellaneous
 178 ----------------
 179
 180 Uvesafb will set a video mode with the default refresh rate and timings
 181 from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
 182
 183
 184 --
 185  Michal Januszewski <spock@gentoo.org>
 186  Last updated: 2009-03-30
 187
 188  Documentation of the uvesafb options is loosely based on vesafb.txt.
 189