Creation of Cybook 2416 (actually Gen4) repository
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Documentation/fb/cyblafb/usage
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Documentation/fb/cyblafb/usage
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CyBlaFB is a framebuffer driver for the Cyberblade/i1 graphics core integrated
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into the VIA Apollo PLE133 (aka vt8601) south bridge. It is developed and
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tested using a VIA EPIA 5000 board.
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Cyblafb - compiled into the kernel or as a module?
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==================================================
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You might compile cyblafb either as a module or compile it permanently into the
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kernel.
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Unless you have a real reason to do so you should not compile both vesafb and
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cyblafb permanently into the kernel. It's possible and it helps during the
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developement cycle, but it's useless and will at least block some otherwise
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usefull memory for ordinary users.
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Selecting Modes
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===============
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Startup Mode
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============
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First of all, you might use the "vga=???" boot parameter as it is
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documented in vesafb.txt and svga.txt. Cyblafb will detect the video
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mode selected and will use the geometry and timings found by
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inspecting the hardware registers.
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video=cyblafb vga=0x317
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Alternatively you might use a combination of the mode, ref and bpp
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parameters. If you compiled the driver into the kernel, add something
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like this to the kernel command line:
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video=cyblafb:1280x1024,bpp=16,ref=50 ...
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If you compiled the driver as a module, the same mode would be
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selected by the following command:
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modprobe cyblafb mode=1280x1024 bpp=16 ref=50 ...
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None of the modes possible to select as startup modes are affected by
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the problems described at the end of the next subsection.
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For all startup modes cyblafb chooses a virtual x resolution of 2048,
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the only exception is mode 1280x1024 in combination with 32 bpp. This
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allows ywrap scrolling for all those modes if rotation is 0 or 2, and
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also fast scrolling if rotation is 1 or 3. The default virtual y reso-
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lution is 4096 for bpp == 8, 2048 for bpp==16 and 1024 for bpp == 32,
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again with the only exception of 1280x1024 at 32 bpp.
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Please do set your video memory size to 8 Mb in the Bios setup. Other
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values will work, but performace is decreased for a lot of modes.
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Mode changes using fbset
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========================
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You might use fbset to change the video mode, see "man fbset". Cyblafb
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generally does assume that you know what you are doing. But it does
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some checks, especially those that are needed to prevent you from
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damaging your hardware.
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- only 8, 16, 24 and 32 bpp video modes are accepted
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- interlaced video modes are not accepted
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- double scan video modes are not accepted
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- if a flat panel is found, cyblafb does not allow you
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to program a resolution higher than the physical
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resolution of the flat panel monitor
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- cyblafb does not allow vclk to exceed 230 MHz. As 32 bpp
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and (currently) 24 bit modes use a doubled vclk internally,
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the dotclock limit as seen by fbset is 115 MHz for those
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modes and 230 MHz for 8 and 16 bpp modes.
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- cyblafb will allow you to select very high resolutions as
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long as the hardware can be programmed to these modes. The
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documented limit 1600x1200 is not enforced, but don't expect
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perfect signal quality.
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Any request that violates the rules given above will be either changed
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to something the hardware supports or an error value will be returned.
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If you program a virtual y resolution higher than the hardware limit,
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cyblafb will silently decrease that value to the highest possible
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value. The same is true for a virtual x resolution that is not
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supported by the hardware. Cyblafb tries to adapt vyres first because
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vxres decides if ywrap scrolling is possible or not.
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Attempts to disable acceleration are ignored, I believe that this is
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safe.
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Some video modes that should work do not work as expected. If you use
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the standard fb.modes, fbset 640x480-60 will program that mode, but
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you will see a vertical area, about two characters wide, with only
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much darker characters than the other characters on the screen.
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Cyblafb does allow that mode to be set, as it does not violate the
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official specifications. It would need a lot of code to reliably sort
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out all invalid modes, playing around with the margin values will
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give a valid mode quickly. And if cyblafb would detect such an invalid
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mode, should it silently alter the requested values or should it
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report an error? Both options have some pros and cons. As stated
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above, none of the startup modes are affected, and if you set
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verbosity to 1 or higher, cyblafb will print the fbset command that
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would be needed to program that mode using fbset.
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Other Parameters
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================
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crt don't autodetect, assume monitor connected to
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standard VGA connector
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fp don't autodetect, assume flat panel display
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connected to flat panel monitor interface
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nativex inform driver about native x resolution of
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flat panel monitor connected to special
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interface (should be autodetected)
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stretch stretch image to adapt low resolution modes to
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higer resolutions of flat panel monitors
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connected to special interface
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center center image to adapt low resolution modes to
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higer resolutions of flat panel monitors
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connected to special interface
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memsize use if autodetected memsize is wrong ...
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should never be necessary
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nopcirr disable PCI read retry
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nopciwr disable PCI write retry
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nopcirb disable PCI read bursts
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nopciwb disable PCI write bursts
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bpp bpp for specified modes
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valid values: 8 || 16 || 24 || 32
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ref refresh rate for specified mode
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valid values: 50 <= ref <= 85
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mode 640x480 or 800x600 or 1024x768 or 1280x1024
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if not specified, the startup mode will be detected
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and used, so you might also use the vga=??? parameter
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described in vesafb.txt. If you do not specify a mode,
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bpp and ref parameters are ignored.
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verbosity 0 is the default, increase to at least 2 for every
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bug report!
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Development hints
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=================
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It's much faster do compile a module and to load the new version after
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unloading the old module than to compile a new kernel and to reboot. So if you
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try to work on cyblafb, it might be a good idea to use cyblafb as a module.
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In real life, fast often means dangerous, and that's also the case here. If
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you introduce a serious bug when cyblafb is compiled into the kernel, the
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kernel will lock or oops with a high probability before the file system is
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mounted, and the danger for your data is low. If you load a broken own version
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of cyblafb on a running system, the danger for the integrity of the file
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system is much higher as you might need a hard reset afterwards. Decide
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yourself.
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Module unloading, the vfb method
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================================
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If you want to unload/reload cyblafb using the virtual framebuffer, you need
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to enable vfb support in the kernel first. After that, load the modules as
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shown below:
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modprobe vfb vfb_enable=1
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modprobe fbcon
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modprobe cyblafb
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fbset -fb /dev/fb1 1280x1024-60 -vyres 2662
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con2fb /dev/fb1 /dev/tty1
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...
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If you now made some changes to cyblafb and want to reload it, you might do it
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as show below:
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con2fb /dev/fb0 /dev/tty1
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...
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rmmod cyblafb
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modprobe cyblafb
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con2fb /dev/fb1 /dev/tty1
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...
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Of course, you might choose another mode, and most certainly you also want to
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map some other /dev/tty* to the real framebuffer device. You might also choose
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to compile fbcon as a kernel module or place it permanently in the kernel.
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I do not know of any way to unload fbcon, and fbcon will prevent the
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framebuffer device loaded first from unloading. [If there is a way, then
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please add a description here!]
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Module unloading, the vesafb method
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===================================
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Configure the kernel:
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<*> Support for frame buffer devices
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[*] VESA VGA graphics support
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<M> Cyberblade/i1 support
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Add e.g. "video=vesafb:ypan vga=0x307" to the kernel parameters. The ypan
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parameter is important, choose any vga parameter you like as long as it is
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a graphics mode.
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After booting, load cyblafb without any mode and bpp parameter and assign
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cyblafb to individual ttys using con2fb, e.g.:
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modprobe cyblafb
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con2fb /dev/fb1 /dev/tty1
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Unloading cyblafb works without problems after you assign vesafb to all
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ttys again, e.g.:
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con2fb /dev/fb0 /dev/tty1
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rmmod cyblafb
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