Root/Documentation/fb/uvesafb.txt

1
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  http://dev.gentoo.org/~spock/projects/uvesafb
19
20Please refer to the v86d documentation for detailed configuration and
21installation instructions.
22
23Note that the v86d userspace helper has to be available at all times in
24order for uvesafb to work properly. If you want to use uvesafb during
25early boot, you will have to include v86d into an initramfs image, and
26either compile it into the kernel or use it as an initrd.
27
282. Caveats and limitations
29--------------------------
30
31uvesafb is a _generic_ driver which supports a wide variety of video
32cards, but which is ultimately limited by the Video BIOS interface.
33The most important limitations are:
34
35- Lack of any type of acceleration.
36- A strict and limited set of supported video modes. Often the native
37  or most optimal resolution/refresh rate for your setup will not work
38  with uvesafb, simply because the Video BIOS doesn't support the
39  video mode you want to use. This can be especially painful with
40  widescreen panels, where native video modes don't have the 4:3 aspect
41  ratio, which is what most BIOS-es are limited to.
42- Adjusting the refresh rate is only possible with a VBE 3.0 compliant
43  Video BIOS. Note that many nVidia Video BIOS-es claim to be VBE 3.0
44  compliant, while they simply ignore any refresh rate settings.
45
463. Configuration
47----------------
48
49uvesafb can be compiled either as a module, or directly into the kernel.
50In both cases it supports the same set of configuration options, which
51are either given on the kernel command line or as module parameters, e.g.:
52
53 video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel)
54
55 # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap (module)
56
57Accepted options:
58
59ypan Enable display panning using the VESA protected mode
60        interface. The visible screen is just a window of the
61        video memory, console scrolling is done by changing the
62        start of the window. This option is available on x86
63        only and is the default option on that architecture.
64
65ywrap Same as ypan, but assumes your gfx board can wrap-around
66        the video memory (i.e. starts reading from top if it
67        reaches the end of video memory). Faster than ypan.
68        Available on x86 only.
69
70redraw Scroll by redrawing the affected part of the screen, this
71        is the default on non-x86.
72
73(If you're using uvesafb as a module, the above three options are
74 used a parameter of the scroll option, e.g. scroll=ypan.)
75
76vgapal Use the standard VGA registers for palette changes.
77
78pmipal Use the protected mode interface for palette changes.
79        This is the default if the protected mode interface is
80        available. Available on x86 only.
81
82mtrr:n Setup memory type range registers for the framebuffer
83        where n:
84              0 - disabled (equivalent to nomtrr) (default)
85              1 - uncachable
86              2 - write-back
87              3 - write-combining
88              4 - write-through
89
90        If you see the following in dmesg, choose the type that matches
91        the old one. In this example, use "mtrr:2".
92...
93mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
94...
95
96nomtrr Do not use memory type range registers.
97
98vremap:n
99        Remap 'n' MiB of video RAM. If 0 or not specified, remap memory
100        according to video mode.
101
102vtotal:n
103        If the video BIOS of your card incorrectly determines the total
104        amount of video RAM, use this option to override the BIOS (in MiB).
105
106<mode> The mode you want to set, in the standard modedb format. Refer to
107        modedb.txt for a detailed description. When uvesafb is compiled as
108        a module, the mode string should be provided as a value of the
109        'mode_option' option.
110
111vbemode:x
112        Force the use of VBE mode x. The mode will only be set if it's
113        found in the VBE-provided list of supported modes.
114        NOTE: The mode number 'x' should be specified in VESA mode number
115        notation, not the Linux kernel one (eg. 257 instead of 769).
116        HINT: If you use this option because normal <mode> parameter does
117        not work for you and you use a X server, you'll probably want to
118        set the 'nocrtc' option to ensure that the video mode is properly
119        restored after console <-> X switches.
120
121nocrtc Do not use CRTC timings while setting the video mode. This option
122        has any effect only if the Video BIOS is VBE 3.0 compliant. Use it
123        if you have problems with modes set the standard way. Note that
124        using this option implies that any refresh rate adjustments will
125        be ignored and the refresh rate will stay at your BIOS default (60 Hz).
126
127noedid Do not try to fetch and use EDID-provided modes.
128
129noblank Disable hardware blanking.
130
131v86d:path
132        Set path to the v86d executable. This option is only available as
133        a module parameter, and not as a part of the video= string. If you
134        need to use it and have uvesafb built into the kernel, use
135        uvesafb.v86d="path".
136
137Additionally, the following parameters may be provided. They all override the
138EDID-provided values and BIOS defaults. Refer to your monitor's specs to get
139the correct values for maxhf, maxvf and maxclk for your hardware.
140
141maxhf:n Maximum horizontal frequency (in kHz).
142maxvf:n Maximum vertical frequency (in Hz).
143maxclk:n Maximum pixel clock (in MHz).
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 (default: /sbin/v86d)
155    Path to the v86d executable. v86d is started by uvesafb
156    if an instance of the daemon isn't already running.
157
158Device attributes:
159
160/sys/bus/platform/drivers/uvesafb/uvesafb.0
161  - nocrtc
162    Use the default refresh rate (60 Hz) if set to 1.
163
164  - oem_product_name
165  - oem_product_rev
166  - oem_string
167  - oem_vendor
168    Information about the card and its maker.
169
170  - vbe_modes
171    A list of video modes supported by the Video BIOS along with their
172    VBE mode numbers in hex.
173
174  - vbe_version
175    A BCD value indicating the implemented VBE standard.
176
1775. Miscellaneous
178----------------
179
180Uvesafb will set a video mode with the default refresh rate and timings
181from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
182
183
184--
185 Michal Januszewski <spock@gentoo.org>
186 Last updated: 2009-03-30
187
188 Documentation of the uvesafb options is loosely based on vesafb.txt.
189
190

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