arm64: add a helper function to traverse arm64_ftr_regs

hulk inclusion
category: feature
bugzilla: NA
CVE: NA

If we want to emulate ID registers, we need to initialize ID registers
firstly.  This commit is to add a helper function to traverse
arm64_ftr_regs so that we can initialize ID registers from
arm64_ftr_regs.
Signed-off-by: Nzhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: NPeng Liang <liangpeng10@huawei.com>
Acked-by: NHanjun Guo <guohanjun@huawei.com>
Reviewed-by: NXiangyou Xie <xiexiangyou@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/arm64/include/asm/cpufeature.h

@@ -89,6 +89,8 @@ struct arm64_ftr_reg {
 
 extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
 
+int arm64_cpu_ftr_regs_traverse(int (*op)(u32, u64, void *), void *argp);
+
 /*
  * CPU capabilities:
  *

arch/arm64/kernel/cpufeature.c

@@ -763,6 +763,19 @@ u64 read_sanitised_ftr_reg(u32 id)
 	return regp->sys_val;
 }
 
+int arm64_cpu_ftr_regs_traverse(int (*op)(u32, u64, void *), void *argp)
+{
+	int i, ret;
+
+	for (i = 0; i <  ARRAY_SIZE(arm64_ftr_regs); i++) {
+		ret = (*op)(arm64_ftr_regs[i].sys_id,
+			    arm64_ftr_regs[i].reg->sys_val, argp);
+		if (ret < 0)
+			return ret;
+	}
+	return 0;
+}
+
 #define read_sysreg_case(r)	\
 	case r:		return read_sysreg_s(r)