WhyCan Forum(哇酷开发者社区)

1. Framebuffer 驅動可以將 Console 輸出導到顯示, 但是, 你必須先開啟 Framebuffer Console 的支援才可以
2. Kernel 參數：console=tty1 console=ttyS0,11520, 代表將 Kernel 輸出訊息輸出到虛擬 Console (tty1) 和 UART (ttyS0)

Framebuffer 驅動在啟動時, 就會去綁定 console (有興趣可以去看 do_take_over_console() 流程), 因此, 當你從 Kernel 參數描述 console=tty1 時, 意思代表輸出的訊息會由 Framebuffer 顯示, 當然, tty1 是虛擬 Console, 你可以只寫：console=tty 就可以~

Linux Kernel 底下有一個 Documentation 資料夾, 相關問題裡面幾乎都會描述, 你可以先看一下, 我幫你抓了三個高度的相關文件給你參考：
https://www.kernel.org/doc/html/latest/fb/fbcon.html
https://www.kernel.org/doc/html/latest/driver-api/console.html
https://tldp.org/HOWTO/Remote-Serial-Console-HOWTO/configure-kernel.html

大概浏览了一下资料，以及司徒大佬发的连接，大概了解流程：简单来说就是lcd属于framebuffer（fb）类设备，内核在注册fb类设备的时候，其中有一步骤就是设置虚拟控制终端（ttyN，N为1 2 3 4 5 6....)与fb设备之间的对应关系，其具体关系摘抄如下：
fbcon=map:<0123>

    This is an interesting option. It tells which driver gets mapped to which console. The value ‘0123’ is a sequence that gets repeated until the total length is 64 which is the number of consoles available. In the above example, it is expanded to 012301230123… and the mapping will be:

    tty | 1 2 3 4 5 6 7 8 9 ...
    fb  | 0 1 2 3 0 1 2 3 0 ...

    ('cat /proc/fb' should tell you what the fb numbers are)

    One side effect that may be useful is using a map value that exceeds the number of loaded fb drivers. For example, if only one driver is available, fb0, adding fbcon=map:1 tells fbcon not to take over the console.

fbcon.c（/home/linux/linux-5.10/drivers/video/fbdev/core/）文件中set_con2fb_map函数负责这个映射过程，该函数简介如下：
/**
*    set_con2fb_map - map console to frame buffer device
*    @unit: virtual console number to map
*    @newidx: frame buffer index to map virtual console to
*      @user: user request
*
*    Maps a virtual console @unit to a frame buffer device
*    @newidx.
*
*    This should be called with the console lock held.
static int set_con2fb_map(int unit, int newidx, int user)
{
    struct vc_data *vc = vc_cons[unit].d;
    int oldidx = con2fb_map[unit];
    struct fb_info *info = registered_fb[newidx];
    struct fb_info *oldinfo = NULL;
    int found, err = 0;

    WARN_CONSOLE_UNLOCKED();

    if (oldidx == newidx)
        return 0;

    if (!info)
        return -EINVAL;

    if (!search_for_mapped_con() || !con_is_bound(&fb_con)) {
        info_idx = newidx;
        return do_fbcon_takeover(0);
    }

    if (oldidx != -1)
        oldinfo = registered_fb[oldidx];

    found = search_fb_in_map(newidx);

    con2fb_map[unit] = newidx;
    if (!err && !found)
        err = con2fb_acquire_newinfo(vc, info, unit, oldidx);

    /*
     * If old fb is not mapped to any of the consoles,
     * fbcon should release it.
     */
    if (!err && oldinfo && !search_fb_in_map(oldidx))
        err = con2fb_release_oldinfo(vc, oldinfo, info, unit, oldidx,
                         found);

    if (!err) {
        int show_logo = (fg_console == 0 && !user &&
                 logo_shown != FBCON_LOGO_DONTSHOW);

        if (!found)
            fbcon_add_cursor_timer(info);
        con2fb_map_boot[unit] = newidx;
        con2fb_init_display(vc, info, unit, show_logo);
    }

    if (!search_fb_in_map(info_idx))
        info_idx = newidx;

    return err;
}

这个问题断断续续查找了给有一星期了，感觉自己还是学艺不精，linux内核知识博大精深，只是有关驱动的部分感觉就足够研究了，感谢司徒大佬的友情帮助。在此发帖记录一下，希望能对后面学习的人有所帮助~