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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
-arches.
-
-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.
-
-vremap:n
- Remap 'n' MiB of video RAM. If 0 or not specified, remap memory
- according to video mode.
-
-vtotal:n
- 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.
-
-vbemode:x
- 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.
-
-v86d:path
- 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:
-
-/sys/bus/platform/drivers/uvesafb
- - 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:
-
-/sys/bus/platform/drivers/uvesafb/uvesafb.0
- - 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.
-