SMP启动分析

SMP启动分析：

主要分为以下几个阶段：

• ROM阶段
• OpenSbi底层初始化阶段
• OpenSbi设备初始化阶段
• • clodboot
• • warmboot
• Linux阶段
• • colboot->启动Linux->在kernel_init中经过层层调用，发送SBI_EXT_HSM_HART_START这个ecall到opensbi；
• • opensbi处理这个ecall将下发参数保存到hartid对应的scratch区域中，发送核间中断，唤醒hartid对应的hart，然后继续执行warmboot的相关流程代码，，最终执行到kernel中；

当CPU上电后，进入ROM阶段

ROM阶段主要进行固件的搬移和参数的准备：

• 设置设备树地址，放入a1寄存器:
• 设置dynamic方式需要的参数，放入a2寄存器存放的地址偏移：

/** Offset of magic member in fw_dynamic_info */
#define FW_DYNAMIC_INFO_MAGIC_OFFSET		(0 * __SIZEOF_POINTER__)
/** Offset of version member in fw_dynamic_info */
#define FW_DYNAMIC_INFO_VERSION_OFFSET		(1 * __SIZEOF_POINTER__)
/** Offset of next_addr member in fw_dynamic_info (version >= 1) */
#define FW_DYNAMIC_INFO_NEXT_ADDR_OFFSET	(2 * __SIZEOF_POINTER__)
/** Offset of next_mode member in fw_dynamic_info  (version >= 1) */
#define FW_DYNAMIC_INFO_NEXT_MODE_OFFSET	(3 * __SIZEOF_POINTER__)
/** Offset of options member in fw_dynamic_info  (version >= 1) */
#define FW_DYNAMIC_INFO_OPTIONS_OFFSET		(4 * __SIZEOF_POINTER__)
/** Offset of boot_hart member in fw_dynamic_info  (version >= 2) */
#define FW_DYNAMIC_INFO_BOOT_HART_OFFSET	(5 * __SIZEOF_POINTER__)

/** Expected value of info magic ('OSBI' ascii string in hex) */
#define FW_DYNAMIC_INFO_MAGIC_VALUE		0x4942534f

• 主要rom阶段要将分配的Cache1和Cache2给关闭，不然会导致后续阶段执行问题；

OpenSbi底层初始化阶段

经过lottery后将选定一个boot hart，其余的hart将等待其重定位和scratch空间和栈空间初始化工作的完成。

_start:
	/* Find preferred boot HART id */
	MOV_3R	s0, a0, s1, a1, s2, a2
	call	fw_boot_hart
	add	a6, a0, zero
	MOV_3R	a0, s0, a1, s1, a2, s2
	li	a7, -1
	beq	a6, a7, _try_lottery
	/* Jump to relocation wait loop if we are not boot hart */
	bne	a0, a6, _wait_relocate_copy_done

_try_lottery:
	/* Jump to relocation wait loop if we don't get relocation lottery */
	la	a6, _relocate_lottery
	li	a7, 1
	amoadd.w a6, a7, (a6)
	bnez	a6, _wait_relocate_copy_done

	/* Save load address */
	la	t0, _load_start
	la	t1, _start
	REG_S	t1, 0(t0)

boot hart在完成fdt的重定位后将进入c阶段

_fdt_reloc_done:

	/* mark boot hart done */
	li	t0, BOOT_STATUS_BOOT_HART_DONE
	la	t1, _boot_status
	REG_S	t0, 0(t1)
	fence	rw, rw
	j	_start_warm

其余的hart在等待BOOT_STATUS_BOOT_HART_DONE标志后，将也会进入c阶段

_wait_for_boot_hart:
	li	t0, BOOT_STATUS_BOOT_HART_DONE
	la	t1, _boot_status
	REG_L	t1, 0(t1)
	/* Reduce the bus traffic so that boot hart may proceed faster */
	nop
	nop
	nop
	bne	t0, t1, _wait_for_boot_hart

OpenSBI设备初始化阶段