Workaround for Neoverse N1 erratum 1868343

Neoverse N1 erratum 1868343 is a Cat B erratum, present in older
revisions of the Neoverse N1 processor core.  The workaround is to
set a bit in the CPUACTLR_EL1 system register, which delays instruction
fetch after branch misprediction. This workaround will have a small
impact on performance.

SDEN can be found here:
https://documentation-service.arm.com/static/5f2c130260a93e65927bc92f

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: I37da2b3b2da697701b883bff9a1eff2772352844

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

@@ -294,6 +294,9 @@ For Neoverse N1, the following errata build flags are defined :
 -  ``ERRATA_N1_1542419``: This applies errata 1542419 workaround to Neoverse-N1
    CPU. This needs to be enabled only for revisions r3p0 - r4p0 of the CPU.
 
+-  ``ERRATA_N1_1868343``: This applies errata 1868343 workaround to Neoverse-N1
+   CPU. This needs to be enabled only for revision <= r4p0 of the CPU.
+
 DSU Errata Workarounds
 ----------------------
 

lib/cpus/aarch64/neoverse_n1.S

@@ -388,6 +388,38 @@ func check_errata_1542419
 	b	cpu_rev_var_range
 endfunc check_errata_1542419
 
+	/* --------------------------------------------------
+	 * Errata Workaround for Neoverse N1 Errata #1868343.
+	 * This applies to revision <= r4p0 of Neoverse N1.
+	 * This workaround is the same as the workaround for
+	 * errata 1262606 and 1275112 but applies to a wider
+	 * revision range.
+	 * Inputs:
+	 * x0: variant[4:7] and revision[0:3] of current cpu.
+	 * Shall clobber: x0-x17
+	 * --------------------------------------------------
+	 */
+func errata_n1_1868343_wa
+	/*
+	 * Compare x0 against revision r4p0
+	 */
+	mov	x17, x30
+	bl	check_errata_1868343
+	cbz	x0, 1f
+	mrs	x1, NEOVERSE_N1_CPUACTLR_EL1
+	orr	x1, x1, NEOVERSE_N1_CPUACTLR_EL1_BIT_13
+	msr	NEOVERSE_N1_CPUACTLR_EL1, x1
+	isb
+1:
+	ret	x17
+endfunc errata_n1_1868343_wa
+
+func check_errata_1868343
+	/* Applies to everything <= r4p0 */
+	mov	x1, #0x40
+	b	cpu_rev_var_ls
+endfunc check_errata_1868343
+
 func neoverse_n1_reset_func
 	mov	x19, x30
 
@@ -462,6 +494,11 @@ func neoverse_n1_reset_func
 	bl	errata_n1_1542419_wa
 #endif
 
+#if ERRATA_N1_1868343
+	mov	x0, x18
+	bl	errata_n1_1868343_wa
+#endif
+
 #if ENABLE_AMU
 	/* Make sure accesses from EL0/EL1 and EL2 are not trapped to EL3 */
 	mrs	x0, actlr_el3
@@ -535,6 +572,7 @@ func neoverse_n1_errata_report
 	report_errata ERRATA_N1_1275112, neoverse_n1, 1275112
 	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_DSU_936184, neoverse_n1, dsu_936184
 
 	ldp	x8, x30, [sp], #16

lib/cpus/cpu-ops.mk

@@ -334,6 +334,10 @@ ERRATA_N1_1315703	?=0
 # to revisions r3p0 - r4p0 of the Neoverse N1 cpu.
 ERRATA_N1_1542419	?=0
 
+# Flag to apply erratum 1868343 workaround during reset. This erratum applies
+# to revision <= r4p0 of the Neoverse N1 cpu.
+ERRATA_N1_1868343	?=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
@@ -603,6 +607,10 @@ $(eval $(call add_define,ERRATA_N1_1315703))
 $(eval $(call assert_boolean,ERRATA_N1_1542419))
 $(eval $(call add_define,ERRATA_N1_1542419))
 
+# Process ERRATA_N1_1868343 flag
+$(eval $(call assert_boolean,ERRATA_N1_1868343))
+$(eval $(call add_define,ERRATA_N1_1868343))
+
 # Process ERRATA_DSU_798953 flag
 $(eval $(call assert_boolean,ERRATA_DSU_798953))
 $(eval $(call add_define,ERRATA_DSU_798953))