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+uvesafb - A Generic Driver for VBE2+ compliant video cards
+1. Requirements
+uvesafb should work with any video card that has a Video BIOS compliant
+with the VBE 2.0 standard.
+Unlike other drivers, uvesafb makes use of a userspace helper called
+v86d. v86d is used to run the x86 Video BIOS code in a simulated and
+controlled environment. This allows uvesafb to function on arches other
+than x86. Check the v86d documentation for a list of currently supported
+v86d source code can be downloaded from the following website:
+ http://dev.gentoo.org/~spock/projects/uvesafb
+Please refer to the v86d documentation for detailed configuration and
+installation instructions.
+Note that the v86d userspace helper has to be available at all times in
+order for uvesafb to work properly. If you want to use uvesafb during
+early boot, you will have to include v86d into an initramfs image, and
+either compile it into the kernel or use it as an initrd.
+2. Caveats and limitations
+uvesafb is a _generic_ driver which supports a wide variety of video
+cards, but which is ultimately limited by the Video BIOS interface.
+The most important limitations are:
+- Lack of any type of acceleration.
+- A strict and limited set of supported video modes. Often the native
+ or most optimal resolution/refresh rate for your setup will not work
+ with uvesafb, simply because the Video BIOS doesn't support the
+ video mode you want to use. This can be especially painful with
+ widescreen panels, where native video modes don't have the 4:3 aspect
+ ratio, which is what most BIOS-es are limited to.
+- Adjusting the refresh rate is only possible with a VBE 3.0 compliant
+ Video BIOS. Note that many nVidia Video BIOS-es claim to be VBE 3.0
+ compliant, while they simply ignore any refresh rate settings.
+3. Configuration
+uvesafb can be compiled either as a module, or directly into the kernel.
+In both cases it supports the same set of configuration options, which
+are either given on the kernel command line or as module parameters, e.g.:
+ video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel)
+ # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap (module)
+Accepted options:
+ypan Enable display panning using the VESA protected mode
+ interface. The visible screen is just a window of the
+ video memory, console scrolling is done by changing the
+ start of the window. This option is available on x86
+ only and is the default option on that architecture.
+ywrap Same as ypan, but assumes your gfx board can wrap-around
+ the video memory (i.e. starts reading from top if it
+ reaches the end of video memory). Faster than ypan.
+ Available on x86 only.
+redraw Scroll by redrawing the affected part of the screen, this
+ is the default on non-x86.
+(If you're using uvesafb as a module, the above three options are
+ used a parameter of the scroll option, e.g. scroll=ypan.)
+vgapal Use the standard VGA registers for palette changes.
+pmipal Use the protected mode interface for palette changes.
+ This is the default if the protected mode interface is
+ available. Available on x86 only.
+mtrr:n Setup memory type range registers for the framebuffer
+ where n:
+ 0 - disabled (equivalent to nomtrr) (default)
+ 1 - uncachable
+ 2 - write-back
+ 3 - write-combining
+ 4 - write-through
+ If you see the following in dmesg, choose the type that matches
+ the old one. In this example, use "mtrr:2".
+mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
+nomtrr Do not use memory type range registers.
+ Remap 'n' MiB of video RAM. If 0 or not specified, remap memory
+ according to video mode.
+ If the video BIOS of your card incorrectly determines the total
+ amount of video RAM, use this option to override the BIOS (in MiB).
+<mode> The mode you want to set, in the standard modedb format. Refer to
+ modedb.txt for a detailed description. When uvesafb is compiled as
+ a module, the mode string should be provided as a value of the
+ 'mode_option' option.
+ Force the use of VBE mode x. The mode will only be set if it's
+ found in the VBE-provided list of supported modes.
+ NOTE: The mode number 'x' should be specified in VESA mode number
+ notation, not the Linux kernel one (eg. 257 instead of 769).
+ HINT: If you use this option because normal <mode> parameter does
+ not work for you and you use a X server, you'll probably want to
+ set the 'nocrtc' option to ensure that the video mode is properly
+ restored after console <-> X switches.
+nocrtc Do not use CRTC timings while setting the video mode. This option
+ has any effect only if the Video BIOS is VBE 3.0 compliant. Use it
+ if you have problems with modes set the standard way. Note that
+ using this option implies that any refresh rate adjustments will
+ be ignored and the refresh rate will stay at your BIOS default (60 Hz).
+noedid Do not try to fetch and use EDID-provided modes.
+noblank Disable hardware blanking.
+ Set path to the v86d executable. This option is only available as
+ a module parameter, and not as a part of the video= string. If you
+ need to use it and have uvesafb built into the kernel, use
+ uvesafb.v86d="path".
+Additionally, the following parameters may be provided. They all override the
+EDID-provided values and BIOS defaults. Refer to your monitor's specs to get
+the correct values for maxhf, maxvf and maxclk for your hardware.
+maxhf:n Maximum horizontal frequency (in kHz).
+maxvf:n Maximum vertical frequency (in Hz).
+maxclk:n Maximum pixel clock (in MHz).
+4. The sysfs interface
+uvesafb provides several sysfs nodes for configurable parameters and
+additional information.
+Driver attributes:
+ - v86d (default: /sbin/v86d)
+ Path to the v86d executable. v86d is started by uvesafb
+ if an instance of the daemon isn't already running.
+Device attributes:
+ - nocrtc
+ Use the default refresh rate (60 Hz) if set to 1.
+ - oem_product_name
+ - oem_product_rev
+ - oem_string
+ - oem_vendor
+ Information about the card and its maker.
+ - vbe_modes
+ A list of video modes supported by the Video BIOS along with their
+ VBE mode numbers in hex.
+ - vbe_version
+ A BCD value indicating the implemented VBE standard.
+5. Miscellaneous
+Uvesafb will set a video mode with the default refresh rate and timings
+from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
+ Michal Januszewski <spock@gentoo.org>
+ Last updated: 2009-03-30
+ Documentation of the uvesafb options is loosely based on vesafb.txt.