linux/Documentation/fb/uvesafb.txt
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   2uvesafb - A Generic Driver for VBE2+ compliant video cards
   3==========================================================
   4
   51. Requirements
   6---------------
   7
   8uvesafb should work with any video card that has a Video BIOS compliant
   9with the VBE 2.0 standard.
  10
  11Unlike other drivers, uvesafb makes use of a userspace helper called
  12v86d.  v86d is used to run the x86 Video BIOS code in a simulated and
  13controlled environment.  This allows uvesafb to function on arches other
  14than x86.  Check the v86d documentation for a list of currently supported
  15arches.
  16
  17v86d source code can be downloaded from the following website:
  18  http://dev.gentoo.org/~spock/projects/uvesafb
  19
  20Please refer to the v86d documentation for detailed configuration and
  21installation instructions.
  22
  23Note that the v86d userspace helper has to be available at all times in
  24order for uvesafb to work properly.  If you want to use uvesafb during
  25early boot, you will have to include v86d into an initramfs image, and
  26either compile it into the kernel or use it as an initrd.
  27
  282. Caveats and limitations
  29--------------------------
  30
  31uvesafb is a _generic_ driver which supports a wide variety of video
  32cards, but which is ultimately limited by the Video BIOS interface.
  33The 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
  463. Configuration
  47----------------
  48
  49uvesafb can be compiled either as a module, or directly into the kernel.
  50In both cases it supports the same set of configuration options, which
  51are 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
  57Accepted options:
  58
  59ypan    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
  65ywrap   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
  70redraw  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
  76vgapal  Use the standard VGA registers for palette changes.
  77
  78pmipal  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
  82mtrr: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...
  93mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
  94...
  95
  96nomtrr  Do not use memory type range registers.
  97
  98vremap:n
  99        Remap 'n' MiB of video RAM.  If 0 or not specified, remap memory
 100        according to video mode.
 101
 102vtotal: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
 111vbemode: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
 121nocrtc  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
 127noedid  Do not try to fetch and use EDID-provided modes.
 128
 129noblank Disable hardware blanking.
 130
 131v86d: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
 137Additionally, the following parameters may be provided.  They all override the
 138EDID-provided values and BIOS defaults.  Refer to your monitor's specs to get
 139the correct values for maxhf, maxvf and maxclk for your hardware.
 140
 141maxhf:n     Maximum horizontal frequency (in kHz).
 142maxvf:n     Maximum vertical frequency (in Hz).
 143maxclk:n    Maximum pixel clock (in MHz).
 144
 1454. The sysfs interface
 146----------------------
 147
 148uvesafb provides several sysfs nodes for configurable parameters and
 149additional information.
 150
 151Driver 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
 158Device 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
 1775. Miscellaneous
 178----------------
 179
 180Uvesafb will set a video mode with the default refresh rate and timings
 181from 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
 190
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