linux-pmac/drivers/video/atyfb.c より
/*
 * Video mode values.
 * These are supposed to be the same as the values that
 * Apple uses in MacOS.
 */
#define VMODE_NVRAM             0       /* use value stored in nvram */
#define VMODE_512_384_60I       1       /* 512x384, 60Hz interlaced (NTSC) */
#define VMODE_512_384_60        2       /* 512x384, 60Hz */
#define VMODE_640_480_50I       3       /* 640x480, 50Hz interlaced (PAL) */
#define VMODE_640_480_60I       4       /* 640x480, 60Hz interlaced (NTSC) */
#define VMODE_640_480_60        5       /* 640x480, 60Hz (VGA) */
#define VMODE_640_480_67        6       /* 640x480, 67Hz */
#define VMODE_640_870_75P       7       /* 640x870, 75Hz (portrait) */
#define VMODE_768_576_50I       8       /* 768x576, 50Hz (PAL full frame) */
#define VMODE_800_600_56        9       /* 800x600, 56Hz */
#define VMODE_800_600_60        10      /* 800x600, 60Hz */
#define VMODE_800_600_72        11      /* 800x600, 72Hz */
#define VMODE_800_600_75        12      /* 800x600, 75Hz */
#define VMODE_832_624_75        13      /* 832x624, 75Hz */
#define VMODE_1024_768_60       14      /* 1024x768, 60Hz */
#define VMODE_1024_768_70       15      /* 1024x768, 70Hz (or 72Hz?) */
#define VMODE_1024_768_75V      16      /* 1024x768, 75Hz (VESA) */
#define VMODE_1024_768_75       17      /* 1024x768, 75Hz */
#define VMODE_1152_870_75       18      /* 1152x870, 75Hz */
#define VMODE_1280_960_75       19      /* 1280x960, 75Hz */
#define VMODE_1280_1024_75      20      /* 1280x1024, 75Hz */
#define VMODE_MAX               20
#define VMODE_CHOOSE            99      /* choose based on monitor sense */