Workaround for Cortex N1 erratum 1946160

Cortex N1 erratum 1946160 is a Cat B erratum present in r0p0, r1p0,
r2p0, r3p0, r3p1, r4p0, and r4p1.  The workaround is to insert a DMB ST
before acquire atomic instructions without release semantics.  This
issue is present starting from r0p0 but this workaround applies to
revisions r3p0, r3p1, r4p0, and r4p1, for previous revisions there is no
workaround.

SDEN can be found here:
https://documentation-service.arm.com/static/5fa9304cd8dacc30eded464f

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: I36e4d6728c275f1c2477dcee9b351077cf7c53e4

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

@@ -310,6 +310,10 @@ For Neoverse N1, the following errata build flags are defined :
 -  ``ERRATA_N1_1868343``: This applies errata 1868343 workaround to Neoverse-N1
    CPU. This needs to be enabled only for revision <= r4p0 of the CPU.
 
+-  ``ERRATA_N1_1946160``: This applies errata 1946160 workaround to Neoverse-N1
+   CPU. This needs to be enabled for revisions r3p0, r3p1, r4p0, and r4p1, for
+   revisions r0p0, r1p0, and r2p0 there is no workaround.
+
 DSU Errata Workarounds
 ----------------------
 

lib/cpus/aarch64/neoverse_n1.S

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2020, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2021, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -407,6 +407,63 @@ func check_errata_1868343
 	b	cpu_rev_var_ls
 endfunc check_errata_1868343
 
+	/* --------------------------------------------------
+	 * Errata Workaround for Neoverse N1 Errata #1946160.
+	 * This applies to revisions r3p0, r3p1, r4p0, and
+	 * r4p1 of Neoverse N1. It also exists in r0p0, r1p0,
+	 * and r2p0 but there is no fix in these revisions.
+	 * Inputs:
+	 * x0: variant[4:7] and revision[0:3] of current cpu.
+	 * Shall clobber: x0-x17
+	 * --------------------------------------------------
+	 */
+func errata_n1_1946160_wa
+	/*
+	 * Compare x0 against r3p0 - r4p1
+	 */
+	mov	x17, x30
+	bl	check_errata_1946160
+	cbz	x0, 1f
+
+	mov	x0, #3
+	msr	S3_6_C15_C8_0, x0
+	ldr	x0, =0x10E3900002
+	msr	S3_6_C15_C8_2, x0
+	ldr	x0, =0x10FFF00083
+	msr	S3_6_C15_C8_3, x0
+	ldr	x0, =0x2001003FF
+	msr	S3_6_C15_C8_1, x0
+
+	mov	x0, #4
+	msr	S3_6_C15_C8_0, x0
+	ldr	x0, =0x10E3800082
+	msr	S3_6_C15_C8_2, x0
+	ldr	x0, =0x10FFF00083
+	msr	S3_6_C15_C8_3, x0
+	ldr	x0, =0x2001003FF
+	msr	S3_6_C15_C8_1, x0
+
+	mov	x0, #5
+	msr	S3_6_C15_C8_0, x0
+	ldr	x0, =0x10E3800200
+	msr	S3_6_C15_C8_2, x0
+	ldr	x0, =0x10FFF003E0
+	msr	S3_6_C15_C8_3, x0
+	ldr	x0, =0x2001003FF
+	msr	S3_6_C15_C8_1, x0
+
+	isb
+1:
+	ret	x17
+endfunc errata_n1_1946160_wa
+
+func check_errata_1946160
+	/* Applies to r3p0 - r4p1. */
+	mov	x1, #0x30
+	mov	x2, #0x41
+	b	cpu_rev_var_range
+endfunc check_errata_1946160
+
 func neoverse_n1_reset_func
 	mov	x19, x30
 
@@ -486,6 +543,11 @@ func neoverse_n1_reset_func
 	bl	errata_n1_1868343_wa
 #endif
 
+#if ERRATA_N1_1946160
+	mov	x0, x18
+	bl	errata_n1_1946160_wa
+#endif
+
 #if ENABLE_AMU
 	/* Make sure accesses from EL0/EL1 and EL2 are not trapped to EL3 */
 	mrs	x0, actlr_el3
@@ -560,6 +622,7 @@ func neoverse_n1_errata_report
 	report_errata ERRATA_N1_1315703, neoverse_n1, 1315703
 	report_errata ERRATA_N1_1542419, neoverse_n1, 1542419
 	report_errata ERRATA_N1_1868343, neoverse_n1, 1868343
+	report_errata ERRATA_N1_1946160, neoverse_n1, 1946160
 	report_errata ERRATA_DSU_936184, neoverse_n1, dsu_936184
 
 	ldp	x8, x30, [sp], #16

lib/cpus/cpu-ops.mk

@@ -355,6 +355,11 @@ ERRATA_N1_1542419	?=0
 # to revision <= r4p0 of the Neoverse N1 cpu.
 ERRATA_N1_1868343	?=0
 
+# Flag to apply erratum 1946160 workaround during reset. This erratum applies
+# to revisions r3p0, r3p1, r4p0, and r4p1 of the Neoverse N1 cpu.  The issue
+# exists in revisions r0p0, r1p0, and r2p0 as well but there is no workaround.
+ERRATA_N1_1946160	?=0
+
 # Flag to apply DSU erratum 798953. This erratum applies to DSUs revision r0p0.
 # Applying the workaround results in higher DSU power consumption on idle.
 ERRATA_DSU_798953	?=0
@@ -644,6 +649,10 @@ $(eval $(call add_define,ERRATA_N1_1542419))
 $(eval $(call assert_boolean,ERRATA_N1_1868343))
 $(eval $(call add_define,ERRATA_N1_1868343))
 
+# Process ERRATA_N1_1946160 flag
+$(eval $(call assert_boolean,ERRATA_N1_1946160))
+$(eval $(call add_define,ERRATA_N1_1946160))
+
 # Process ERRATA_DSU_798953 flag
 $(eval $(call assert_boolean,ERRATA_DSU_798953))
 $(eval $(call add_define,ERRATA_DSU_798953))