fix(cpus): workaround for Neoverse-N2 erratum 3701773

Neoverse-N2 erratum 3701773 that applies to r0p0, r0p1, r0p2 and r0p3
is still Open.

The workaround is for EL3 software that performs context save/restore
on a change of Security state to use a value of SCR_EL3.NS when
accessing ICH_VMCR_EL2 that reflects the Security state that owns the
data being saved or restored.

SDEN documentation:
https://developer.arm.com/documentation/SDEN-1982442/latest/

Change-Id: If95bd67363228c8083724b31f630636fb27f3b61
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>

docs/design/cpu-specific-build-macros.rst

@@ -728,6 +728,10 @@ For Neoverse N2, the following errata build flags are defined :
    CPU. This needs to be enabled for revisions r0p0, r0p1 and r0p2. It is fixed
    in r0p3.
 
+-  ``ERRATA_N2_3701773``: This applies errata 3701773 workaround to Neoverse-N2
+   CPU. This needs to be enabled for revisions r0p0, r0p1, r0p2, r0p3 and is
+   still open.
+
 For Cortex-X2, the following errata build flags are defined :
 
 -  ``ERRATA_X2_2002765``: This applies errata 2002765 workaround to Cortex-X2

include/lib/cpus/aarch64/neoverse_n2.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2023, Arm Limited. All rights reserved.
+ * Copyright (c) 2020-2025, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -69,4 +69,8 @@
 #define CPUECTLR2_EL1_TXREQ_LSB				U(0)
 #define CPUECTLR2_EL1_TXREQ_WIDTH			U(3)
 
+#ifndef __ASSEMBLER__
+long check_erratum_neoverse_n2_3701773(long cpu_rev);
+#endif /* __ASSEMBLER__ */
+
 #endif /* NEOVERSE_N2_H */

lib/cpus/aarch64/neoverse_n2.S

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2024, Arm Limited. All rights reserved.
+ * Copyright (c) 2020-2025, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -20,6 +20,12 @@
 #error "Neoverse-N2 supports only AArch64. Compile with CTX_INCLUDE_AARCH32_REGS=0"
 #endif
 
+.global check_erratum_neoverse_n2_3701773
+
+add_erratum_entry neoverse_n2, ERRATUM(3701773), ERRATA_N2_3701773, NO_APPLY_AT_RESET
+
+check_erratum_ls neoverse_n2, ERRATUM(3701773), CPU_REV(0, 3)
+
 #if WORKAROUND_CVE_2022_23960
 	wa_cve_2022_23960_bhb_vector_table NEOVERSE_N2_BHB_LOOP_COUNT, neoverse_n2
 #endif /* WORKAROUND_CVE_2022_23960 */

lib/cpus/cpu-ops.mk

@@ -728,6 +728,11 @@ CPU_FLAG_LIST += ERRATA_N2_2743089
 # to r0p0, r0p1, r0p2 of the Neoverse N2 cpu, it is fixed in r0p3.
 CPU_FLAG_LIST += ERRATA_N2_2779511
 
+# Flag to apply erratum 3701773 workaround during context save/restore of
+# ICH_VMCR_EL2 reg. This erratum applies to revisions r0p0, r0p1, r0p2 and r0p3
+# of the Neoverse N2 cpu and is still open.
+CPU_FLAG_LIST += ERRATA_N2_3701773
+
 # Flag to apply erratum 2002765 workaround during reset. This erratum applies
 # to revisions r0p0, r1p0, and r2p0 of the Cortex-X2 cpu and is still open.
 CPU_FLAG_LIST += ERRATA_X2_2002765

lib/cpus/errata_common.c

@@ -21,6 +21,7 @@
 #include <cortex_x925.h>
 #include <lib/cpus/cpu_ops.h>
 #include <lib/cpus/errata.h>
+#include <neoverse_n2.h>
 
 #if ERRATA_A520_2938996 || ERRATA_X4_2726228
 unsigned int check_if_affected_core(void)
@@ -114,6 +115,14 @@ bool errata_ich_vmcr_el2_applies(void)
 			return true;
 		break;
 #endif /* ERRATA_X925_3701747 */
+
+#if ERRATA_N2_3701773
+	case EXTRACT_PARTNUM(NEOVERSE_N2_MIDR):
+		if (check_erratum_neoverse_n2_3701773(cpu_get_rev_var()) == ERRATA_APPLIES)
+			return true;
+		break;
+#endif /* ERRATA_N2_3701773 */
+
 	default:
 		break;
 	}