一、方法1修改内核

kernal/include/linux/serial_core.h

...
#define UART_XMIT_SIZE 	PAGE_SIZE
...

kernal/include/generated/asm-offsets.h

...
#define PAGE_SIZE	4096
...

注意：
2.6的内核PAGE_SIZE的位置在kernal/include/asm/page.h

二、方法2应用层修改
使用:ioctl(fd, TIOCSSERIAL, &serial);

#define FRAME_SIZE 10
struct serial_struct serial; 
...
serial.xmit_fifo_size = FIFO_SIZE; // what is "xmit" ?? 
ioctl(fd, TIOCSSERIAL, &serial); 
...

完整参考程序

#include <asm-generic/ioctl.h>
#include <termios.h>
#include <linux/serial.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
 
int UartBuffSizeSet(char *dev_path,int size) {  
  int ret;
  int fd =  open(dev_path, O_RDWR | O_NOCTTY | O_NONBLOCK);
  if(fd < 0){
    return -1;
  }
  struct serial_struct serial;
  ret = ioctl(fd, TIOCGSERIAL, &serial);
  if (ret != 0) {
    close(fd);
    return -2;
  }+
  serial.xmit_fifo_size = 1024*1024; //1M
  ret = ioctl(fd, TIOCSSERIAL, &serial);
  if(ret != 0) {
    close(fd);
    return -3;
  }
  close(fd);
  return 0;
}