fix(cpus): workaround for Neoverse-N2 erratum 2326639

Neoverse-N2 erratum 2326639 is a Cat B erratum that applies to revision
r0p0 and is fixed in r0p1. The workaround is to set CPUACTLR2_EL1[36] to
1 before the power down sequence that sets CORE_PWRDN_EN. This allows
the cpu to retry the power down and prevents the deadlock. TF-A never
clears this bit even if it wakes up from the wfi in the sequence since
it is not expected to do anything but retry to power down after and the
bit is cleared on reset.

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

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: I9a325c5b9b498798e5efd5c79a4a6d5bed97c619

2 files changed, 44 insertions, 0 deletions

diff --git a/lib/cpus/aarch64/neoverse_n2.S b/lib/cpus/aarch64/neoverse_n2.S
index 72e5ca816..5861decbb 100644
--- a/lib/cpus/aarch64/neoverse_n2.S
+++ b/lib/cpus/aarch64/neoverse_n2.S
@@ -338,6 +338,34 @@ func check_errata_2280757
 	b	cpu_rev_var_ls
 endfunc check_errata_2280757
 
+/* --------------------------------------------------
+ * Errata Workaround for Neoverse N2 Erratum 2326639.
+ * This applies to revision r0p0 of Neoverse N2,
+ * fixed in r0p1.
+ * Inputs:
+ * x0: variant[4:7] and revision[0:3] of current cpu.
+ * Shall clobber: x0-x1, x17
+ * --------------------------------------------------
+ */
+func errata_n2_2326639_wa
+	/* Check revision. */
+	mov	x17, x30
+	bl	check_errata_2326639
+	cbz	x0, 1f
+
+	/* Set bit 36 in ACTLR2_EL1 */
+	mrs	x1, NEOVERSE_N2_CPUACTLR2_EL1
+	orr	x1, x1, #NEOVERSE_N2_CPUACTLR2_EL1_BIT_36
+	msr	NEOVERSE_N2_CPUACTLR2_EL1, x1
+1:
+	ret	x17
+endfunc errata_n2_2326639_wa
+
+func check_errata_2326639
+	/* Applies to r0p0, fixed in r0p1 */
+	mov	x1, #0x00
+	b	cpu_rev_var_ls
+endfunc check_errata_2326639
 
 /* --------------------------------------------------
  * Errata Workaround for Neoverse N2 Erratum 2376738.
@@ -533,6 +561,13 @@ func neoverse_n2_reset_func
 endfunc neoverse_n2_reset_func
 
 func neoverse_n2_core_pwr_dwn
+#if ERRATA_N2_2326639
+	mov	x15, x30
+	bl	cpu_get_rev_var
+	bl	errata_n2_2326639_wa
+	mov	x30, x15
+#endif /* ERRATA_N2_2326639 */
+
 	/* ---------------------------------------------------
 	 * Enable CPU power down bit in power control register
 	 * No need to do cache maintenance here.
@@ -569,6 +604,7 @@ func neoverse_n2_errata_report
 	report_errata ERRATA_N2_2138958, neoverse_n2, 2138958
 	report_errata ERRATA_N2_2242400, neoverse_n2, 2242400
 	report_errata ERRATA_N2_2280757, neoverse_n2, 2280757
+	report_errata ERRATA_N2_2326639, neoverse_n2, 2326639
 	report_errata ERRATA_N2_2376738, neoverse_n2, 2376738
 	report_errata ERRATA_N2_2388450, neoverse_n2, 2388450
 	report_errata WORKAROUND_CVE_2022_23960, neoverse_n2, cve_2022_23960
diff --git a/lib/cpus/cpu-ops.mk b/lib/cpus/cpu-ops.mk
index ec0d95e7d..2c42ad082 100644
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@@ -592,6 +592,10 @@ ERRATA_N2_2242400	?=0
 # to revision r0p0 of the Neoverse N2 cpu and is still open.
 ERRATA_N2_2280757	?=0
 
+# Flag to apply erraturm 2326639 workaroud during powerdown. This erratum
+# applies to revision r0p0 of the Neoverse N2 cpu and is fixed in r0p1.
+ERRATA_N2_2326639	?=0
+
 # Flag to apply erratum 2376738 workaround during reset. This erratum applies
 # to revision r0p0 of the Neoverse N2 cpu, it is fixed in r0p1.
 ERRATA_N2_2376738	?=0
@@ -1200,6 +1204,10 @@ $(eval $(call add_define,ERRATA_N2_2242400))
 $(eval $(call assert_boolean,ERRATA_N2_2280757))
 $(eval $(call add_define,ERRATA_N2_2280757))
 
+# Process ERRATA_N2_2326639 flag
+$(eval $(call assert_boolean,ERRATA_N2_2326639))
+$(eval $(call add_define,ERRATA_N2_2326639))
+
 # Process ERRATA_N2_2376738 flag
 $(eval $(call assert_boolean,ERRATA_N2_2376738))
 $(eval $(call add_define,ERRATA_N2_2376738))