path: root/Documentation/fb/modedb.txt
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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/fb/modedb.txt
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+ modedb default video mode support
+Currently all frame buffer device drivers have their own video mode databases,
+which is a mess and a waste of resources. The main idea of modedb is to have
+ - one routine to probe for video modes, which can be used by all frame buffer
+ devices
+ - one generic video mode database with a fair amount of standard videomodes
+ (taken from XFree86)
+ - the possibility to supply your own mode database for graphics hardware that
+ needs non-standard modes, like amifb and Mac frame buffer drivers (which
+ use macmodes.c)
+When a frame buffer device receives a video= option it doesn't know, it should
+consider that to be a video mode option. If no frame buffer device is specified
+in a video= option, fbmem considers that to be a global video mode option.
+Valid mode specifiers (mode_option argument):
+ <xres>x<yres>[-<bpp>][@<refresh>]
+ <name>[-<bpp>][@<refresh>]
+with <xres>, <yres>, <bpp> and <refresh> decimal numbers and <name> a string.
+Things between square brackets are optional.
+To find a suitable video mode, you just call
+int __init fb_find_mode(struct fb_var_screeninfo *var,
+ struct fb_info *info, const char *mode_option,
+ const struct fb_videomode *db, unsigned int dbsize,
+ const struct fb_videomode *default_mode,
+ unsigned int default_bpp)
+with db/dbsize your non-standard video mode database, or NULL to use the
+standard video mode database.
+fb_find_mode() first tries the specified video mode (or any mode that matches,
+e.g. there can be multiple 640x480 modes, each of them is tried). If that
+fails, the default mode is tried. If that fails, it walks over all modes.
+To specify a video mode at bootup, use the following boot options:
+ video=<driver>:<xres>x<yres>[-<bpp>][@refresh]
+where <driver> is a name from the table below. Valid default modes can be
+found in linux/drivers/video/modedb.c. Check your driver's documentation.
+There may be more modes.
+ Drivers that support modedb boot options
+ Boot Name Cards Supported
+ amifb - Amiga chipset frame buffer
+ aty128fb - ATI Rage128 / Pro frame buffer
+ atyfb - ATI Mach64 frame buffer
+ tdfxfb - 3D Fx frame buffer
+ tridentfb - Trident (Cyber)blade chipset frame buffer
+BTW, only a few drivers use this at the moment. Others are to follow
+(feel free to send patches).

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