控制台乱码问题调试笔记
平台：P2020RDB
问题描述：从u-boot到内核启动执行init进程之前，串口控制台输出正常，之后串口控制台输出出现乱码，最后启动到用户登录界面时控制台输出恢复正常。
解决过程：
1.首先对比内核启动信息，发现出现乱码的位置是位于串口硬件初始化之后
Serial: 8250/16550 driver, 2 ports, IRQ sharing enabled
serial8250.0: ttyS0 at MMIO 0xffe04500 (irq = 42) is a 16550A
console [ttyS0] enabled, bootconsole disabled
console [ttyS0] enabled, bootconsole disabled
brd: module loaded乱码前的最后正常输出是：
Serial: 8250/16550 driver, 2 ports, IRQ sharing enabled
2.分析后面的的输出信息，可以得到下面这些结论：
乱码过程发生在bootconsole到real console切换的过程中
3.第一句不正常的输出是
serial8250.0: ttyS0 at MMIO 0xffe04500 (irq = 42) is a 16550A这句话应该是在uart_report_port函数中输出的，但此时console切换还没发生，之所以此处未能正正确输出，是因为此条信息保存在buf内，等到此条信息输出到控制台时，控制台已经切换，并在切换过程中发生了串口波特率的设置bug
static inline void
uart_report_port(struct uart_driver *drv, struct uart_port *port)
{
char address[64];
switch (port->iotype) {
case UPIO_PORT:
snprintf(address, sizeof(address), "I/O 0x%lx", port->iobase);
break;
case UPIO_HUB6:
snprintf(address, sizeof(address),
"I/O 0x%lx offset 0x%x", port->iobase, port->hub6);
break;
case UPIO_MEM:
case UPIO_MEM32:
case UPIO_AU:
case UPIO_TSI:
case UPIO_DWAPB:
snprintf(address, sizeof(address),
"MMIO 0x%llx", (unsigned long long)port->mapbase);
break;
default:
strlcpy(address, "*unknown*", sizeof(address));
break;
}
printk(KERN_INFO "%s%s%s%d at %s (irq = %d) is a %s\n",
port->dev ? dev_name(port->dev) : "",
port->dev ? ": " : "",
drv->dev_name,
drv->tty_driver->name_base + port->line,
address, port->irq, uart_type(port));
}
4.串口控制台的切换在函数register_console.
void register_console(struct console *newcon)
{
int i;
unsigned long flags;
struct console *bcon = NULL;
/*
* before we register a new CON_BOOT console, make sure we don't
* already have a valid console
*/
if (console_drivers && newcon->flags & CON_BOOT) {
/* find the last or real console */
for_each_console(bcon) {
if (!(bcon->flags & CON_BOOT)) {
printk(KERN_INFO "Too late to register bootconsole %s%d\n",
newcon->name, newcon->index);
return;
}
}
}
if (console_drivers && console_drivers->flags & CON_BOOT)
bcon = console_drivers;
if (preferred_console < 0 || bcon || !console_drivers)
preferred_console = selected_console;
if (newcon->early_setup)
newcon->early_setup();
/*
* See if we want to use this console driver. If we
* didn't select a console we take the first one
* that registers here.
*/
if (preferred_console < 0) {
if (newcon->index < 0)
newcon->index = 0;
if (newcon->setup == NULL ||
newcon->setup(newcon, NULL) == 0) {
newcon->flags |= CON_ENABLED;
if (newcon->device) {
newcon->flags |= CON_CONSDEV;
preferred_console = 0;
}
}
}
/*
* See if this console matches one we selected on
* the command line.
*/
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)
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))
return;
/*
* If we have a bootconsole, and are switching to a real console,
* don't print everything out again, since when the boot console, and
* the real console are the same physical device, it's annoying to
* see the beginning boot messages twice
*/
if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
newcon->flags &= ~CON_PRINTBUFFER;
/*
* Put this console in the list - keep the
* preferred driver at the head of the list.
*/
acquire_console_sem();
if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
newcon->next = console_drivers;
console_drivers = newcon;
if (newcon->next)
newcon->next->flags &= ~CON_CONSDEV;
} else {
newcon->next = console_drivers->next;
console_drivers->next = newcon;
}
if (newcon->flags & CON_PRINTBUFFER) {
/*
* release_console_sem() will print out the buffered messages
* for us.
*/
spin_lock_irqsave(&logbuf_lock, flags);
con_start = log_start;
spin_unlock_irqrestore(&logbuf_lock, flags);
}
release_console_sem();
/*
* By unregistering the bootconsoles after we enable the real console
* we get the "console xxx enabled" message on all the consoles -
* boot consoles, real consoles, etc - this is to ensure that end
* users know there might be something in the kernel's log buffer that
* went to the bootconsole (that they do not see on the real console)
*/
if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
/* we need to iterate through twice, to make sure we print
* everything out, before we unregister the console(s)
*/
printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
newcon->name, newcon->index);
for_each_console(bcon)
if (bcon->flags & CON_BOOT)
unregister_console(bcon);
} else {
printk(KERN_INFO "%sconsole [%s%d] enabled\n",
(newcon->flags & CON_BOOT) ? "boot" : "" ,
newcon->name, newcon->index);
}
}在register_console函数里面调用了newcon->setup（），分析代码这个setup函数是硬件相关的8250的串口setup函数:serial8250_console_setup
static int __init serial8250_console_setup(struct console *co, char *options)
{
struct uart_port *port;
int baud = 9600;
int bits = 8;
int parity = 'n';
int flow = 'n';
/*
* Check whether an invalid uart number has been specified, and
* if so, search for the first available port that does have
* console support.
*/
if (co->index >= nr_uarts)
co->index = 0;
port = &serial8250_ports[co->index].port;
if (!port->iobase && !port->membase)
return -ENODEV;
if (options)
uart_parse_options(options, &baud, &parity, &bits, &flow);
return uart_set_options(port, co, baud, parity, bits, flow);
}
我的项目问题就出现在下面的代码
if (options)
uart_parse_options(options, &baud, &parity, &bits, &flow);
options，是从u-boot传入的启动参数里面会有串口的波特率设置，但是我的项目的u-boot在RAM中直接加载内核时，启动参数没有能够正确传送到内核。
workaround是在在set之前重新设置baud的数值，与u-boot一致
if (options)
uart_parse_options(options, &baud, &parity, &bits, &flow);
baud = 115200
return uart_set_options(port, co, baud, parity, bits, flow);