fix(errata): workaround for Neoverse-N2 erratum 2138958

Neoverse-N2 erratum 2138958 is a Cat B erratum that applies to
revision r0p0 of CPU. It is still open. The workaround
is to set CPUACTLR5_EL1[13] to 1'b1.

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

Signed-off-by: nayanpatel-arm <nayankumar.patel@arm.com>
Change-Id: I5247f8f8eef08d38c169aad6d2c5501ac387c720

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

@@ -423,6 +423,9 @@ For Neoverse N2, the following errata build flags are defined :
 -  ``ERRATA_N2_2242415``: This applies errata 2242415 workaround to Neoverse-N2
    CPU. This needs to be enabled for revision r0p0 of the CPU and is still open.
 
+-  ``ERRATA_N2_2138958``: This applies errata 2138958 workaround to Neoverse-N2
+   CPU. This needs to be enabled for revision r0p0 of the CPU and is still open.
+
 DSU Errata Workarounds
 ----------------------
 

include/lib/cpus/aarch64/neoverse_n2.h

@@ -41,6 +41,7 @@
  ******************************************************************************/
 #define NEOVERSE_N2_CPUACTLR5_EL1			S3_0_C15_C8_0
 #define NEOVERSE_N2_CPUACTLR5_EL1_BIT_44		(ULL(1) << 44)
+#define NEOVERSE_N2_CPUACTLR5_EL1_BIT_13		(ULL(1) << 13)
 
 /*******************************************************************************
  * CPU Auxiliary Control register specific definitions.

lib/cpus/aarch64/neoverse_n2.S

@@ -240,6 +240,34 @@ func check_errata_2138953
 	b	cpu_rev_var_ls
 endfunc check_errata_2138953
 
+/* --------------------------------------------------
+ * Errata Workaround for Neoverse N2 Erratum 2138958.
+ * This applies to revision r0p0 of Neoverse N2. it is still open.
+ * Inputs:
+ * x0: variant[4:7] and revision[0:3] of current cpu.
+ * Shall clobber: x0-x1, x17
+ * --------------------------------------------------
+ */
+func errata_n2_2138958_wa
+	/* Check revision. */
+	mov	x17, x30
+	bl	check_errata_2138958
+	cbz	x0, 1f
+
+	/* Apply instruction patching sequence */
+	mrs	x1, NEOVERSE_N2_CPUACTLR5_EL1
+	orr	x1, x1, NEOVERSE_N2_CPUACTLR5_EL1_BIT_13
+	msr	NEOVERSE_N2_CPUACTLR5_EL1, x1
+1:
+	ret	x17
+endfunc errata_n2_2138958_wa
+
+func check_errata_2138958
+	/* Applies to r0p0 */
+	mov	x1, #0x00
+	b	cpu_rev_var_ls
+endfunc check_errata_2138958
+
 	/* -------------------------------------------
 	 * The CPU Ops reset function for Neoverse N2.
 	 * -------------------------------------------
@@ -291,6 +319,11 @@ func neoverse_n2_reset_func
 	bl	errata_n2_2242415_wa
 #endif
 
+#if ERRATA_N2_2138958
+	mov	x0, x18
+	bl	errata_n2_2138958_wa
+#endif
+
 #if ENABLE_AMU
 	/* Make sure accesses from EL0/EL1 and EL2 are not trapped to EL3 */
 	mrs	x0, cptr_el3
@@ -358,6 +391,7 @@ func neoverse_n2_errata_report
 	report_errata ERRATA_N2_2138956, neoverse_n2, 2138956
 	report_errata ERRATA_N2_2138953, neoverse_n2, 2138953
 	report_errata ERRATA_N2_2242415, neoverse_n2, 2242415
+	report_errata ERRATA_N2_2138958, neoverse_n2, 2138958
 
 	ldp	x8, x30, [sp], #16
 	ret

lib/cpus/cpu-ops.mk

@@ -465,6 +465,10 @@ ERRATA_N2_2138953	?=0
 # to revision r0p0 of the Neoverse N2 cpu and is still open.
 ERRATA_N2_2242415	?=0
 
+# Flag to apply erratum 2138958 workaround during reset. This erratum applies
+# to revision r0p0 of the Neoverse N2 cpu and is still open.
+ERRATA_N2_2138958	?=0
+
 # Flag to apply erratum 2055002 workaround during reset. This erratum applies
 # to revision r1p0, r2p0 of the Cortex-A710 cpu and is still open.
 ERRATA_A710_2055002	?=0
@@ -870,6 +874,10 @@ $(eval $(call add_define,ERRATA_N2_2138953))
 $(eval $(call assert_boolean,ERRATA_N2_2242415))
 $(eval $(call add_define,ERRATA_N2_2242415))
 
+# Process ERRATA_N2_2138958 flag
+$(eval $(call assert_boolean,ERRATA_N2_2138958))
+$(eval $(call add_define,ERRATA_N2_2138958))
+
 # Process ERRATA_A710_2055002 flag
 $(eval $(call assert_boolean,ERRATA_A710_2055002))
 $(eval $(call add_define,ERRATA_A710_2055002))