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+uvesafb - A Generic Driver for VBE2+ compliant video cards
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+==========================================================
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+
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+1. Requirements
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+---------------
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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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+
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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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+
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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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+
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+Please refer to the v86d documentation for detailed configuration and
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+installation instructions.
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+
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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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+
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+2. Caveats and limitations
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+--------------------------
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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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+
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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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+
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+3. Configuration
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+----------------
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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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+
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+ video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel)
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+
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+ # modprobe uvesafb mode=1024x768-32 mtrr=3 scroll=ywrap (module)
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+
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+Accepted options:
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+
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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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+
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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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+
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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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+
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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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+
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+vgapal Use the standard VGA registers for palette changes.
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+
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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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+
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+mtrr:n Setup memory type range registers for the framebuffer
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+ where n:
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+ 0 - disabled (equivalent to nomtrr) (default)
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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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+
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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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+
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+nomtrr Do not use memory type range registers.
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+
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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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+
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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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+
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+<mode> 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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+
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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 <mode> 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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+
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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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+
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+noedid Do not try to fetch and use EDID-provided modes.
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+
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+noblank Disable hardware blanking.
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+
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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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+
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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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+
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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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+
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+4. The sysfs interface
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+----------------------
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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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+
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+Driver attributes:
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+
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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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+
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+Device attributes:
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+
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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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+
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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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+
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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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+
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+ - vbe_version
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+ A BCD value indicating the implemented VBE standard.
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+
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+5. Miscellaneous
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+----------------
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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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+
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+--
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+ Michal Januszewski <spock@gentoo.org>
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+ Last updated: 2007-06-16
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+
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+ Documentation of the uvesafb options is loosely based on vesafb.txt.
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+
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Michal Januszewski