平台移植的部分分析

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Regulation:

Don’t care the multiple processor for the moment;

All code analysis is based the ARM architecture;

2008-2-29

Begin from the setup_arch(), it is called by the start_kernel().

void __init setup_arch(char **cmdline_p)

{

struct tag *tags = (struct tag *)&init_tags;

struct machine_desc *mdesc;

char *from = default_command_line;

setup_processor();

mdesc = setup_machine(machine_arch_type);

machine_name = mdesc->name;

if (mdesc->soft_reboot)

reboot_setup("s");

if (mdesc->boot_params)

tags = phys_to_virt(mdesc->boot_params);

* If we have the old style parameters, convert them to

* a tag list.

if (tags->hdr.tag != ATAG_CORE)

convert_to_tag_list(tags);

if (tags->hdr.tag != ATAG_CORE)

tags = (struct tag *)&init_tags;

if (mdesc->fixup)

mdesc->fixup(mdesc, tags, &from, &meminfo);

if (tags->hdr.tag == ATAG_CORE) {

if (meminfo.nr_banks != 0)

squash_mem_tags(tags);

parse_tags(tags);

}

init_mm.start_code = (unsigned long) &_text;

init_mm.end_code = (unsigned long) &_etext;

init_mm.end_data = (unsigned long) &_edata;

init_mm.brk = (unsigned long) &_end;

memcpy(saved_command_line, from, COMMAND_LINE_SIZE);

saved_command_line[COMMAND_LINE_SIZE-1] = '/0';

parse_cmdline(cmdline_p, from);

paging_init(&meminfo, mdesc);

request_standard_resources(&meminfo, mdesc);

cpu_init();

* Set up various architecture-specific pointers

init_arch_irq = mdesc->init_irq;

system_timer = mdesc->timer;

init_machine = mdesc->init_machine;

#ifdef CONFIG_VT

#if defined(CONFIG_VGA_CONSOLE)

conswitchp = &vga_con;

#elif defined(CONFIG_DUMMY_CONSOLE)

conswitchp = &dummy_con;

#endif

}

setup_processor():This function get the processor information.

lookup_processor_type() It is defined in the file “head.s”, it get the processor information which defined in the proc-*.s. for example, in arch/arm/mm/proc-v6.s,define the armv6 processor information as follows:

__v6_proc_info:

.long 0x0007b000

.long 0x0007f000

.long PMD_TYPE_SECT | /

PMD_SECT_BUFFERABLE | /

PMD_SECT_CACHEABLE | /

PMD_SECT_AP_WRITE | /

PMD_SECT_AP_READ

b __v6_setup

.long cpu_arch_name

.long cpu_elf_name

.long cpu_v6_name

.long v6_processor_functions

.long v6wbi_tlb_fns

.long v6_user_fns

.long v6_cache_fns

.size __v6_proc_info, . - __v6_proc_info

If the processor is based ARMV6(The platform I used is MX31,it is based ARM11 that is ARMV6 architecture), after call the lookup_processor_type(), the variable list will point to the __v6_proc_info, the printk will print the processor information like this:

“CPU: Some Random V6 Processor [4107b364] revision 4 (ARMv6TEJ)”

At last, call the function cpu_proc_init(), it is defined in the file /include/asm-arm/cpu-multi32.h:

#define cpu_proc_init() processor._proc_init()

The processor information is in the proc-v6.s, of course, the proc_init too, it is the cpu_v6_proc_init.

static void __init setup_processor(void)

{

struct proc_info_list *list;

* locate processor in the list of supported processor

* types. The linker builds this table for us from the

* entries in arch/arm/mm/proc-*.S

list = lookup_processor_type();

if (!list) {

printk("CPU configuration botched (ID %08x), unable "

"to continue./n", processor_id);

while (1);

}

cpu_name = list->cpu_name;

#ifdef MULTI_CPU

processor = *list->proc;

#endif

#ifdef MULTI_TLB

cpu_tlb = *list->tlb;

#endif

#ifdef MULTI_USER

cpu_user = *list->user;

#endif

#ifdef MULTI_CACHE

cpu_cache = *list->cache;

#endif

printk("CPU: %s [%08x] revision %d (ARMv%s)/n",

cpu_name, processor_id, (int)processor_id & 15,

proc_arch[cpu_architecture()]);

sprintf(system_utsname.machine, "%s%c", list->arch_name, ENDIANNESS);

sprintf(elf_platform, "%s%c", list->elf_name, ENDIANNESS);

elf_hwcap = list->elf_hwcap;

cpu_proc_init();

}

setup_machine(): just like the setup_processor(),it is get the machine descriptor, the machine descriptor is defined in the platform file which path is /arch/arm/mach-*/

static struct machine_desc * __init setup_machine(unsigned int nr)

{

struct machine_desc *list;

* locate machine in the list of supported machines.

list = lookup_machine_type(nr);

if (!list) {

printk("Machine configuration botched (nr %d), unable "

"to continue./n", nr);

while (1);

}

printk("Machine: %s/n", list->name);

return list;

}

lookup_machine_type(): it is defined in the head.s too.

The parameter machine_arch_type is defined in /include/asm-arm/Match-type.h, it is different in different platform.

reboot_setup(): Set the soft boot mode, my platform doesn’t initialize the soft_reboot, so it doesn’t call it.

If your platform have the boot parameter, the tags will point its address, otherwise it will point to the default tag init_tags. Because the boot parameter is physical address, it need to be change to virtual address.

if (mdesc->boot_params)

tags = phys_to_virt(mdesc->boot_params);

If we have a old style parameters, convert them to the tag list, if the conversion is fail, still use the default tags.

if (tags->hdr.tag != ATAG_CORE)

convert_to_tag_list(tags);

if (tags->hdr.tag != ATAG_CORE)

tags = (struct tag *)&init_tags;