errata: workaround for Neoverse N2 erratum 2067956

Neoverse N2 erratum 2067956 is a Cat B erratum that applies to
revision r0p0 and is still open. The workaround is to set
CPUACTLR_EL1[46] to force L2 tag ECC inline correction mode.
This workaround works on revision r0p0.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN1982442/latest

Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
Change-Id: Ie92d18a379c66675b5c1c50fd0b8dde130848b21

4 files changed, 55 insertions, 4 deletions

diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 9b8b0be94..1f998922b 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -378,6 +378,11 @@ For Cortex-A710, the following errata build flags are defined :
    Cortex-A710 CPU. This needs to be enabled only for revisions r0p0, r1p0 and
    r2p0 of the CPU. It is still open.
 
+For Neoverse N2, the following errata build flags are defined :
+
+-  ``ERRATA_N2_2067956``: This applies errata 2067956 workaround to Neoverse-N2
+   CPU. This needs to be enabled for revision r0p0 of the CPU and is still open.
+
 DSU Errata Workarounds
 ----------------------
 
diff --git a/include/lib/cpus/aarch64/neoverse_n2.h b/include/lib/cpus/aarch64/neoverse_n2.h
index 7cbd8c17b..a7211d218 100644
--- a/include/lib/cpus/aarch64/neoverse_n2.h
+++ b/include/lib/cpus/aarch64/neoverse_n2.h
@@ -25,6 +25,12 @@
 /*******************************************************************************
  * CPU Auxiliary Control register specific definitions.
  ******************************************************************************/
+#define NEOVERSE_N2_CPUACTLR_EL1		S3_0_C15_C1_0
+#define NEOVERSE_N2_CPUACTLR_EL1_BIT_46	        (ULL(1) << 46)
+
+/*******************************************************************************
+ * CPU Auxiliary Control register 2 specific definitions.
+ ******************************************************************************/
 #define NEOVERSE_N2_CPUACTLR2_EL1		S3_0_C15_C1_1
 #define NEOVERSE_N2_CPUACTLR2_EL1_BIT_2		(ULL(1) << 2)
 
diff --git a/lib/cpus/aarch64/neoverse_n2.S b/lib/cpus/aarch64/neoverse_n2.S
index 44db0b3a3..1ab5412b1 100644
--- a/lib/cpus/aarch64/neoverse_n2.S
+++ b/lib/cpus/aarch64/neoverse_n2.S
@@ -61,6 +61,32 @@ func check_errata_2002655
 	b	cpu_rev_var_ls
 endfunc check_errata_2002655
 
+/* ---------------------------------------------------------------
+ * Errata Workaround for Neoverse N2 Erratum 2067956.
+ * This applies to revision r0p0 of Neoverse N2 and is still open.
+ * Inputs:
+ * x0: variant[4:7] and revision[0:3] of current cpu.
+ * Shall clobber: x0-x17
+ * ---------------------------------------------------------------
+ */
+func errata_n2_2067956_wa
+	/* Compare x0 against revision r0p0 */
+	mov	x17, x30
+	bl	check_errata_2067956
+	cbz	x0, 1f
+	mrs	x1, NEOVERSE_N2_CPUACTLR_EL1
+	orr	x1, x1, NEOVERSE_N2_CPUACTLR_EL1_BIT_46
+	msr	NEOVERSE_N2_CPUACTLR_EL1, x1
+1:
+	ret	x17
+endfunc errata_n2_2067956_wa
+
+func check_errata_2067956
+	/* Applies to r0p0 */
+	mov	x1, #0x00
+	b	cpu_rev_var_ls
+endfunc check_errata_2067956
+
 	/* -------------------------------------------------
 	 * The CPU Ops reset function for Neoverse N2.
 	 * -------------------------------------------------
@@ -81,6 +107,11 @@ func neoverse_n2_reset_func
 	orr	x0, x0, #NEOVERSE_N2_CPUACTLR2_EL1_BIT_2
 	msr	NEOVERSE_N2_CPUACTLR2_EL1, x0
 
+#if ERRATA_N2_2067956
+	mov	x0, x18
+	bl	errata_n2_2067956_wa
+#endif
+
 #if ENABLE_AMU
 	/* Make sure accesses from EL0/EL1 and EL2 are not trapped to EL3 */
 	mrs	x0, cptr_el3
@@ -97,9 +128,9 @@ func neoverse_n2_reset_func
 
 #if NEOVERSE_Nx_EXTERNAL_LLC
 	/* Some systems may have External LLC, core needs to be made aware */
-	mrs     x0, NEOVERSE_N2_CPUECTLR_EL1
-	orr     x0, x0, NEOVERSE_N2_CPUECTLR_EL1_EXTLLC_BIT
-	msr     NEOVERSE_N2_CPUECTLR_EL1, x0
+	mrs	x0, NEOVERSE_N2_CPUECTLR_EL1
+	orr	x0, x0, NEOVERSE_N2_CPUECTLR_EL1_EXTLLC_BIT
+	msr	NEOVERSE_N2_CPUECTLR_EL1, x0
 #endif
 
 	bl	cpu_get_rev_var
@@ -111,7 +142,7 @@ func neoverse_n2_reset_func
 #endif
 
 	isb
-	ret x19
+	ret	x19
 endfunc neoverse_n2_reset_func
 
 func neoverse_n2_core_pwr_dwn
@@ -142,6 +173,7 @@ func neoverse_n2_errata_report
 	 * checking functions of each errata.
 	 */
 	report_errata ERRATA_N2_2002655, neoverse_n2, 2002655
+	report_errata ERRATA_N2_2067956, neoverse_n2, 2067956
 
 	ldp	x8, x30, [sp], #16
 	ret
diff --git a/lib/cpus/cpu-ops.mk b/lib/cpus/cpu-ops.mk
index 73f977b37..b8576e9b5 100644
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@@ -421,6 +421,10 @@ ERRATA_A710_1987031	?=0
 # to revisions r0p0, r1p0 and r2p0 of the Cortex-A710 cpu and is still open.
 ERRATA_A710_2081180	?=0
 
+# Flag to apply erratum 2067956 workaround during reset. This erratum applies
+# to revision r0p0 of the Neoverse N2 cpu and is still open.
+ERRATA_N2_2067956	?=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
@@ -774,6 +778,10 @@ $(eval $(call add_define,ERRATA_A710_1987031))
 $(eval $(call assert_boolean,ERRATA_A710_2081180))
 $(eval $(call add_define,ERRATA_A710_2081180))
 
+# Process ERRATA_N2_2067956 flag
+$(eval $(call assert_boolean,ERRATA_N2_2067956))
+$(eval $(call add_define,ERRATA_N2_2067956))
+
 # Process ERRATA_DSU_798953 flag
 $(eval $(call assert_boolean,ERRATA_DSU_798953))
 $(eval $(call add_define,ERRATA_DSU_798953))