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uvesafb - A Generic Driver for VBE2+ compliant video cards
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==========================================================
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1. Requirements
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---------------
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uvesafb should work with any video card that has a Video BIOS compliant
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with the VBE 2.0 standard.
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Unlike other drivers, uvesafb makes use of a userspace helper called
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v86d.  v86d is used to run the x86 Video BIOS code in a simulated and
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controlled environment.  This allows uvesafb to function on arches other
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than x86.  Check the v86d documentation for a list of currently supported
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arches.
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v86d source code can be downloaded from the following website:
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  http://dev.gentoo.org/~spock/projects/uvesafb
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Please refer to the v86d documentation for detailed configuration and
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installation instructions.
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Note that the v86d userspace helper has to be available at all times in
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order for uvesafb to work properly.  If you want to use uvesafb during
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early boot, you will have to include v86d into an initramfs image, and
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either compile it into the kernel or use it as an initrd.
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2. Caveats and limitations
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--------------------------
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uvesafb is a _generic_ driver which supports a wide variety of video
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cards, but which is ultimately limited by the Video BIOS interface.
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The most important limitations are:
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- Lack of any type of acceleration.
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- A strict and limited set of supported video modes.  Often the native
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  or most optimal resolution/refresh rate for your setup will not work
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  with uvesafb, simply because the Video BIOS doesn't support the
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  video mode you want to use.  This can be especially painful with
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  widescreen panels, where native video modes don't have the 4:3 aspect
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  ratio, which is what most BIOS-es are limited to.
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- Adjusting the refresh rate is only possible with a VBE 3.0 compliant
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  Video BIOS.  Note that many nVidia Video BIOS-es claim to be VBE 3.0
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  compliant, while they simply ignore any refresh rate settings.
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3. Configuration
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----------------
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uvesafb can be compiled either as a module, or directly into the kernel.
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In both cases it supports the same set of configuration options, which
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are either given on the kernel command line or as module parameters, e.g.:
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 video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel)
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 # modprobe uvesafb mode=1024x768-32 mtrr=3 scroll=ywrap  (module)
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Accepted options:
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ypan    Enable display panning using the VESA protected mode
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        interface.  The visible screen is just a window of the
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        video memory, console scrolling is done by changing the
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        start of the window.  Available on x86 only.
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ywrap   Same as ypan, but assumes your gfx board can wrap-around
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        the video memory (i.e. starts reading from top if it
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        reaches the end of video memory).  Faster than ypan.
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        Available on x86 only.
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redraw  Scroll by redrawing the affected part of the screen, this
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        is the safe (and slow) default.
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(If you're using uvesafb as a module, the above three options are
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 used a parameter of the scroll option, e.g. scroll=ypan.)
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vgapal  Use the standard VGA registers for palette changes.
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pmipal  Use the protected mode interface for palette changes.
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        This is the default if the protected mode interface is
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        available.  Available on x86 only.
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mtrr:n  Setup memory type range registers for the framebuffer
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        where n:
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              1 - uncachable
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              2 - write-back
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              3 - write-combining
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              4 - write-through
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        If you see the following in dmesg, choose the type that matches
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        the old one.  In this example, use "mtrr:2".
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...
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mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
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...
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nomtrr  Do not use memory type range registers.
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vremap:n
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        Remap 'n' MiB of video RAM.  If 0 or not specified, remap memory
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        according to video mode.
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vtotal:n
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        If the video BIOS of your card incorrectly determines the total
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        amount of video RAM, use this option to override the BIOS (in MiB).
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  The mode you want to set, in the standard modedb format.  Refer to
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        modedb.txt for a detailed description.  When uvesafb is compiled as
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        a module, the mode string should be provided as a value of the
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        'mode' option.
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vbemode:x
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        Force the use of VBE mode x.  The mode will only be set if it's
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        found in the VBE-provided list of supported modes.
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        NOTE: The mode number 'x' should be specified in VESA mode number
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        notation, not the Linux kernel one (eg. 257 instead of 769).
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        HINT: If you use this option because normal  parameter does
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        not work for you and you use a X server, you'll probably want to
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        set the 'nocrtc' option to ensure that the video mode is properly
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        restored after console <-> X switches.
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nocrtc  Do not use CRTC timings while setting the video mode.  This option
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        has any effect only if the Video BIOS is VBE 3.0 compliant.  Use it
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        if you have problems with modes set the standard way.  Note that
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        using this option implies that any refresh rate adjustments will
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        be ignored and the refresh rate will stay at your BIOS default (60 Hz).
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noedid  Do not try to fetch and use EDID-provided modes.
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noblank Disable hardware blanking.
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v86d:path
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        Set path to the v86d executable. This option is only available as
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        a module parameter, and not as a part of the video= string.  If you
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        need to use it and have uvesafb built into the kernel, use
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        uvesafb.v86d="path".
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Additionally, the following parameters may be provided.  They all override the
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EDID-provided values and BIOS defaults.  Refer to your monitor's specs to get
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the correct values for maxhf, maxvf and maxclk for your hardware.
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maxhf:n     Maximum horizontal frequency (in kHz).
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maxvf:n     Maximum vertical frequency (in Hz).
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maxclk:n    Maximum pixel clock (in MHz).
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4. The sysfs interface
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----------------------
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uvesafb provides several sysfs nodes for configurable parameters and
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additional information.
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Driver attributes:
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/sys/bus/platform/drivers/uvesafb
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  - v86d (default: /sbin/v86d)
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    Path to the v86d executable. v86d is started by uvesafb
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    if an instance of the daemon isn't already running.
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Device attributes:
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/sys/bus/platform/drivers/uvesafb/uvesafb.0
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  - nocrtc
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    Use the default refresh rate (60 Hz) if set to 1.
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  - oem_product_name
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  - oem_product_rev
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  - oem_string
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  - oem_vendor
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    Information about the card and its maker.
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  - vbe_modes
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    A list of video modes supported by the Video BIOS along with their
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    VBE mode numbers in hex.
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  - vbe_version
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    A BCD value indicating the implemented VBE standard.
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5. Miscellaneous
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----------------
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Uvesafb will set a video mode with the default refresh rate and timings
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from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
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--
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 Michal Januszewski 
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 Last updated: 2007-06-16
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 Documentation of the uvesafb options is loosely based on vesafb.txt.
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