lib: Allow overriding SBI implementation ID

Ideally, the SBI implementation ID for OpenSBI should always be
0x1 (as mentioned in SBI v0.2 spec) but external firmware (such
as EDK2) which use OpenSBI as library might want to override the
SBI implementation ID with their custom implementation ID.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

include/sbi/sbi_ecall.h

@@ -42,6 +42,10 @@ u16 sbi_ecall_version_major(void);
 
 u16 sbi_ecall_version_minor(void);
 
+unsigned long sbi_ecall_get_impid(void);
+
+void sbi_ecall_set_impid(unsigned long impid);
+
 struct sbi_ecall_extension *sbi_ecall_find_extension(unsigned long extid);
 
 int sbi_ecall_register_extension(struct sbi_ecall_extension *ext);

lib/sbi/sbi_ecall.c

@@ -22,6 +22,18 @@ u16 sbi_ecall_version_minor(void)
 	return SBI_ECALL_VERSION_MINOR;
 }
 
+static unsigned long ecall_impid = SBI_OPENSBI_IMPID;
+
+unsigned long sbi_ecall_get_impid(void)
+{
+	return ecall_impid;
+}
+
+void sbi_ecall_set_impid(unsigned long impid)
+{
+	ecall_impid = impid;
+}
+
 static SBI_LIST_HEAD(ecall_exts_list);
 
 struct sbi_ecall_extension *sbi_ecall_find_extension(unsigned long extid)

lib/sbi/sbi_ecall_base.c

@@ -46,7 +46,7 @@ static int sbi_ecall_base_handler(unsigned long extid, unsigned long funcid,
 		*out_val = *out_val | SBI_ECALL_VERSION_MINOR;
 		break;
 	case SBI_EXT_BASE_GET_IMP_ID:
-		*out_val = SBI_OPENSBI_IMPID;
+		*out_val = sbi_ecall_get_impid();
 		break;
 	case SBI_EXT_BASE_GET_IMP_VERSION:
 		*out_val = OPENSBI_VERSION;