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authorMichal Januszewski <spock@gentoo.org>2007-10-16 04:28:28 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-16 12:43:14 -0400
commit0a0b53f66043b4f4da728b391232de5e5d22f145 (patch)
tree19f5a27cff9e07adb10f88657a786c26b9aa175b /Documentation/fb
parent8bdb3a2d7df48b861972c4bfb58490853a228f51 (diff)
uvesafb: documentation
Documentation for the uvesafb driver. Signed-off-by: Michal Januszewski <spock@gentoo.org> Signed-off-by: Antonino Daplas <adaplas@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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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=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. Available on x86 only.
63
64ywrap Same as ypan, but assumes your gfx board can wrap-around
65 the video memory (i.e. starts reading from top if it
66 reaches the end of video memory). Faster than ypan.
67 Available on x86 only.
68
69redraw Scroll by redrawing the affected part of the screen, this
70 is the safe (and slow) default.
71
72(If you're using uvesafb as a module, the above three options are
73 used a parameter of the scroll option, e.g. scroll=ypan.)
74
75vgapal Use the standard VGA registers for palette changes.
76
77pmipal Use the protected mode interface for palette changes.
78 This is the default if the protected mode interface is
79 available. Available on x86 only.
80
81mtrr:n Setup memory type range registers for the framebuffer
82 where n:
83 0 - disabled (equivalent to nomtrr) (default)
84 1 - uncachable
85 2 - write-back
86 3 - write-combining
87 4 - write-through
88
89 If you see the following in dmesg, choose the type that matches
90 the old one. In this example, use "mtrr:2".
91...
92mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
93...
94
95nomtrr Do not use memory type range registers.
96
97vremap:n
98 Remap 'n' MiB of video RAM. If 0 or not specified, remap memory
99 according to video mode.
100
101vtotal:n
102 If the video BIOS of your card incorrectly determines the total
103 amount of video RAM, use this option to override the BIOS (in MiB).
104
105<mode> The mode you want to set, in the standard modedb format. Refer to
106 modedb.txt for a detailed description. When uvesafb is compiled as
107 a module, the mode string should be provided as a value of the
108 'mode' option.
109
110vbemode:x
111 Force the use of VBE mode x. The mode will only be set if it's
112 found in the VBE-provided list of supported modes.
113 NOTE: The mode number 'x' should be specified in VESA mode number
114 notation, not the Linux kernel one (eg. 257 instead of 769).
115 HINT: If you use this option because normal <mode> parameter does
116 not work for you and you use a X server, you'll probably want to
117 set the 'nocrtc' option to ensure that the video mode is properly
118 restored after console <-> X switches.
119
120nocrtc Do not use CRTC timings while setting the video mode. This option
121 has any effect only if the Video BIOS is VBE 3.0 compliant. Use it
122 if you have problems with modes set the standard way. Note that
123 using this option implies that any refresh rate adjustments will
124 be ignored and the refresh rate will stay at your BIOS default (60 Hz).
125
126noedid Do not try to fetch and use EDID-provided modes.
127
128noblank Disable hardware blanking.
129
130v86d:path
131 Set path to the v86d executable. This option is only available as
132 a module parameter, and not as a part of the video= string. If you
133 need to use it and have uvesafb built into the kernel, use
134 uvesafb.v86d="path".
135
136Additionally, the following parameters may be provided. They all override the
137EDID-provided values and BIOS defaults. Refer to your monitor's specs to get
138the correct values for maxhf, maxvf and maxclk for your hardware.
139
140maxhf:n Maximum horizontal frequency (in kHz).
141maxvf:n Maximum vertical frequency (in Hz).
142maxclk:n Maximum pixel clock (in MHz).
143
1444. The sysfs interface
145----------------------
146
147uvesafb provides several sysfs nodes for configurable parameters and
148additional information.
149
150Driver attributes:
151
152/sys/bus/platform/drivers/uvesafb
153 - v86d (default: /sbin/v86d)
154 Path to the v86d executable. v86d is started by uvesafb
155 if an instance of the daemon isn't already running.
156
157Device attributes:
158
159/sys/bus/platform/drivers/uvesafb/uvesafb.0
160 - nocrtc
161 Use the default refresh rate (60 Hz) if set to 1.
162
163 - oem_product_name
164 - oem_product_rev
165 - oem_string
166 - oem_vendor
167 Information about the card and its maker.
168
169 - vbe_modes
170 A list of video modes supported by the Video BIOS along with their
171 VBE mode numbers in hex.
172
173 - vbe_version
174 A BCD value indicating the implemented VBE standard.
175
1765. Miscellaneous
177----------------
178
179Uvesafb will set a video mode with the default refresh rate and timings
180from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
181
182
183--
184 Michal Januszewski <spock@gentoo.org>
185 Last updated: 2007-06-16
186
187 Documentation of the uvesafb options is loosely based on vesafb.txt.
188