extern void mach_prepare_shutdown(void);
 
 /* environment arguments from bootloader */
-extern unsigned long bus_clock, cpu_clock_freq;
+extern unsigned long cpu_clock_freq;
 extern unsigned long memsize, highmemsize;
 
 /* loongson-specific command line, env and memory initialization */
 
 
 #include <loongson.h>
 
-unsigned long bus_clock, cpu_clock_freq;
+unsigned long cpu_clock_freq;
 EXPORT_SYMBOL(cpu_clock_freq);
 unsigned long memsize, highmemsize;
 
-/* pmon passes arguments in 32bit pointers */
-int *_prom_envp;
-
 #define parse_even_earlier(res, option, p)                             \
 do {                                                                   \
        if (strncmp(option, (char *)p, strlen(option)) == 0)            \
 
 void __init prom_init_env(void)
 {
+       /* pmon passes arguments in 32bit pointers */
+       int *_prom_envp;
+       unsigned long bus_clock;
+       unsigned int processor_id;
        long l;
 
        /* firmware arguments are initialized in head.S */
        }
        if (memsize == 0)
                memsize = 256;
+       if (bus_clock == 0)
+               bus_clock = 66000000;
+       if (cpu_clock_freq == 0) {
+               processor_id = (¤t_cpu_data)->processor_id;
+               switch (processor_id & PRID_REV_MASK) {
+               case PRID_REV_LOONGSON2E:
+                       cpu_clock_freq = 533080000;
+                       break;
+               case PRID_REV_LOONGSON2F:
+                       cpu_clock_freq = 797000000;
+                       break;
+               default:
+                       cpu_clock_freq = 100000000;
+                       break;
+               }
+       }
 
        pr_info("busclock=%ld, cpuclock=%ld, memsize=%ld, highmemsize=%ld\n",
                bus_clock, cpu_clock_freq, memsize, highmemsize);