linux/Documentation/fb/uvesafb.rst
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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
  19  https://github.com/mjanusz/v86d
  20
  21Please refer to the v86d documentation for detailed configuration and
  22installation instructions.
  23
  24Note that the v86d userspace helper has to be available at all times in
  25order for uvesafb to work properly.  If you want to use uvesafb during
  26early boot, you will have to include v86d into an initramfs image, and
  27either compile it into the kernel or use it as an initrd.
  28
  292. Caveats and limitations
  30--------------------------
  31
  32uvesafb is a _generic_ driver which supports a wide variety of video
  33cards, but which is ultimately limited by the Video BIOS interface.
  34The most important limitations are:
  35
  36- Lack of any type of acceleration.
  37- A strict and limited set of supported video modes.  Often the native
  38  or most optimal resolution/refresh rate for your setup will not work
  39  with uvesafb, simply because the Video BIOS doesn't support the
  40  video mode you want to use.  This can be especially painful with
  41  widescreen panels, where native video modes don't have the 4:3 aspect
  42  ratio, which is what most BIOS-es are limited to.
  43- Adjusting the refresh rate is only possible with a VBE 3.0 compliant
  44  Video BIOS.  Note that many nVidia Video BIOS-es claim to be VBE 3.0
  45  compliant, while they simply ignore any refresh rate settings.
  46
  473. Configuration
  48----------------
  49
  50uvesafb can be compiled either as a module, or directly into the kernel.
  51In both cases it supports the same set of configuration options, which
  52are either given on the kernel command line or as module parameters, e.g.::
  53
  54 video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel)
  55
  56 # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap  (module)
  57
  58Accepted options:
  59
  60======= =========================================================
  61ypan    Enable display panning using the VESA protected mode
  62        interface.  The visible screen is just a window of the
  63        video memory, console scrolling is done by changing the
  64        start of the window.  This option is available on x86
  65        only and is the default option on that architecture.
  66
  67ywrap   Same as ypan, but assumes your gfx board can wrap-around
  68        the video memory (i.e. starts reading from top if it
  69        reaches the end of video memory).  Faster than ypan.
  70        Available on x86 only.
  71
  72redraw  Scroll by redrawing the affected part of the screen, this
  73        is the default on non-x86.
  74======= =========================================================
  75
  76(If you're using uvesafb as a module, the above three options are
  77used a parameter of the scroll option, e.g. scroll=ypan.)
  78
  79=========== ====================================================================
  80vgapal      Use the standard VGA registers for palette changes.
  81
  82pmipal      Use the protected mode interface for palette changes.
  83            This is the default if the protected mode interface is
  84            available.  Available on x86 only.
  85
  86mtrr:n      Setup memory type range registers for the framebuffer
  87            where n:
  88
  89                - 0 - disabled (equivalent to nomtrr)
  90                - 3 - write-combining (default)
  91
  92            Values other than 0 and 3 will result in a warning and will be
  93            treated just like 3.
  94
  95nomtrr      Do not use memory type range registers.
  96
  97vremap:n
  98            Remap 'n' MiB of video RAM.  If 0 or not specified, remap memory
  99            according to video mode.
 100
 101vtotal:n    If the video BIOS of your card incorrectly determines the total
 102            amount of video RAM, use this option to override the BIOS (in MiB).
 103
 104<mode>      The mode you want to set, in the standard modedb format.  Refer to
 105            modedb.txt for a detailed description.  When uvesafb is compiled as
 106            a module, the mode string should be provided as a value of the
 107            'mode_option' option.
 108
 109vbemode:x   Force the use of VBE mode x.  The mode will only be set if it's
 110            found in the VBE-provided list of supported modes.
 111            NOTE: The mode number 'x' should be specified in VESA mode number
 112            notation, not the Linux kernel one (eg. 257 instead of 769).
 113            HINT: If you use this option because normal <mode> parameter does
 114            not work for you and you use a X server, you'll probably want to
 115            set the 'nocrtc' option to ensure that the video mode is properly
 116            restored after console <-> X switches.
 117
 118nocrtc      Do not use CRTC timings while setting the video mode.  This option
 119            has any effect only if the Video BIOS is VBE 3.0 compliant.  Use it
 120            if you have problems with modes set the standard way.  Note that
 121            using this option implies that any refresh rate adjustments will
 122            be ignored and the refresh rate will stay at your BIOS default
 123            (60 Hz).
 124
 125noedid      Do not try to fetch and use EDID-provided modes.
 126
 127noblank     Disable hardware blanking.
 128
 129v86d:path   Set path to the v86d executable. This option is only available as
 130            a module parameter, and not as a part of the video= string.  If you
 131            need to use it and have uvesafb built into the kernel, use
 132            uvesafb.v86d="path".
 133=========== ====================================================================
 134
 135Additionally, the following parameters may be provided.  They all override the
 136EDID-provided values and BIOS defaults.  Refer to your monitor's specs to get
 137the correct values for maxhf, maxvf and maxclk for your hardware.
 138
 139=========== ======================================
 140maxhf:n     Maximum horizontal frequency (in kHz).
 141maxvf:n     Maximum vertical frequency (in Hz).
 142maxclk:n    Maximum pixel clock (in MHz).
 143=========== ======================================
 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
 155    (default: /sbin/v86d)
 156
 157    Path to the v86d executable. v86d is started by uvesafb
 158    if an instance of the daemon isn't already running.
 159
 160Device attributes:
 161
 162/sys/bus/platform/drivers/uvesafb/uvesafb.0
 163  nocrtc
 164    Use the default refresh rate (60 Hz) if set to 1.
 165
 166  oem_product_name, oem_product_rev, oem_string, 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
 1765. Miscellaneous
 177----------------
 178
 179Uvesafb will set a video mode with the default refresh rate and timings
 180from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
 181
 182
 183
 184 Michal Januszewski <spock@gentoo.org>
 185
 186 Last updated: 2017-10-10
 187
 188 Documentation of the uvesafb options is loosely based on vesafb.txt.
 189