printk如何定向输出到UART的?
printk如何定向输出到UART的?
我们通常在config里面配置这么一句“CONFIG_CMDLINE="console=tty0 console=ttyMT3,921600n1 root=/dev/ram"”,然后修改console的赋值就可以改变输出的位置,代码中如何实现的呢?这里紧接着上文中的printk.c文件中,有这么一个函数先看一下:
/*
* Set up a list of consoles. Called from init/main.c
*/
拉风的注释直接告诉了我们这个函数被init/main.c文件中某个函数调用。
- static int __init console_setup(char *str)
- {
- char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
- char *s, *options, *brl_options = NULL;
- int idx;
- #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
- if (!memcmp(str, "brl,", 4)) {
- brl_options = "";
- str += 4;
- } else if (!memcmp(str, "brl=", 4)) {
- brl_options = str + 4;
- str = strchr(brl_options, ',');
- if (!str) {
- printk(KERN_ERR "need port name after brl=\n");
- return 1;
- }
- *(str++) = 0;
- }
- #endif
- /*
- * Decode str into name, index, options.
- */
- if (str[0] >= '0' && str[0] <= '9') {
- strcpy(buf, "ttyS");
- strncpy(buf + 4, str, sizeof(buf) - 5);
- } else {
- strncpy(buf, str, sizeof(buf) - 1);
- }
- buf[sizeof(buf) - 1] = 0;
- if ((options = strchr(str, ',')) != NULL)
- *(options++) = 0;
- #ifdef __sparc__
- if (!strcmp(str, "ttya"))
- strcpy(buf, "ttyS0");
- if (!strcmp(str, "ttyb"))
- strcpy(buf, "ttyS1");
- #endif
- for (s = buf; *s; s++)
- if ((*s >= '0' && *s <= '9') || *s == ',')
- break;
- idx = simple_strtoul(s, NULL, 10);
- *s = 0;
- __add_preferred_console(buf, idx, options, brl_options);
- console_set_on_cmdline = 1;
- return 1;
- }
- __setup("console=", console_setup);
- /*
- * The console driver calls this routine during kernel initialization
- * to register the console printing procedure with printk() and to
- * print any messages that were printed by the kernel before the
- * console driver was initialized.
- *
- * This can happen pretty early during the boot process (because of
- * early_printk) - sometimes before setup_arch() completes - be careful
- * of what kernel features are used - they may not be initialised yet.
- *
- * There are two types of consoles - bootconsoles (early_printk) and
- * "real" consoles (everything which is not a bootconsole) which are
- * handled differently.
- * - Any number of bootconsoles can be registered at any time.
- * - As soon as a "real" console is registered, all bootconsoles
- * will be unregistered automatically.
- * - Once a "real" console is registered, any attempt to register a
- * bootconsoles will be rejected
- */
- void register_console(struct console *newcon)
- {
- ............................
- /*
- * See if this console matches one we selected on
- * the command line.
- */
- //看上面的注释我们也可以知道了command line中的定义在这里也起作用了
- for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
- i++) {
- if (strcmp(console_cmdline[i].name, newcon->name) != 0)
- continue;
- if (newcon->index >= 0 &&
- newcon->index != console_cmdline[i].index)
- continue;
- if (newcon->index < 0)
- newcon->index = console_cmdline[i].index;
- #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
- if (console_cmdline[i].brl_options) {
- newcon->flags |= CON_BRL;
- braille_register_console(newcon,
- console_cmdline[i].index,
- console_cmdline[i].options,
- console_cmdline[i].brl_options);
- return;
- }
- #endif
- if (newcon->setup &&
- newcon->setup(newcon, console_cmdline[i].options) != 0)/////在这里可以看到setup的过程了
- break;
- newcon->flags |= CON_ENABLED;
- newcon->index = console_cmdline[i].index;
- if (i == selected_console) {
- newcon->flags |= CON_CONSDEV;
- preferred_console = selected_console;
- }
- break;
- }
- if (!(newcon->flags & CON_ENABLED))//其他的console driver屏蔽掉
- return;
- ........................................
- }
到了这里,so command line的tty端口的指定就到了这里了。
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