fix(cpus): workaround for Cortex-X2 erratum 2768515

Cortex-X2 erratum 2768515 is a Cat B erratum that applies to
all revisions <=r2p1 and is still open. The workaround is to
insert a dsb before the isb in the power down sequence.

SDEN documentation:
https://developer.arm.com/documentation/SDEN1775100/latest

Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
Change-Id: Ib02688f7b6dc7f6ec305e68e8895174f6fd577a0
(cherry picked from commit 1cfde82227558a8cc1792c068bc7a7cdf8feab43)

3 files changed, 44 insertions, 0 deletions

diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 368da0aec..c07a0aa16 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -599,6 +599,10 @@ For Cortex-X2, the following errata build flags are defined :
    Cortex-X2 CPU. This needs to be enabled for revisions r0p0, r1p0 and r2p0
    of the CPU and is fixed in r2p1.
 
+-  ``ERRATA_X2_2768515``: This applies errata 2768515 workaround to
+   Cortex-X2 CPU. This needs to be enabled for revisions r0p0, r1p0, r2p0
+   and r2p1 of the CPU and is still open.
+
 For Cortex-X3, the following errata build flags are defined :
 
 - ``ERRATA_X3_2313909``: This applies errata 2313909 workaround to
diff --git a/lib/cpus/aarch64/cortex_x2.S b/lib/cpus/aarch64/cortex_x2.S
index c810be6b0..f56d50a34 100644
--- a/lib/cpus/aarch64/cortex_x2.S
+++ b/lib/cpus/aarch64/cortex_x2.S
@@ -295,6 +295,30 @@ func check_errata_2371105
 	b	cpu_rev_var_ls
 endfunc check_errata_2371105
 
+/* ----------------------------------------------------
+ * Errata Workaround for Cortex-X2 Errata #2768515
+ * This applies to revisions <= r2p1 and is still open.
+ * x0: variant[4:7] and revision[0:3] of current cpu.
+ * Shall clobber: x0-x17
+ * ----------------------------------------------------
+ */
+func errata_x2_2768515_wa
+	mov	x17, x30
+	bl	check_errata_2768515
+	cbz	x0, 1f
+
+	/* dsb before isb of power down sequence */
+	dsb	sy
+1:
+	ret	x17
+endfunc errata_x2_2768515_wa
+
+func check_errata_2768515
+	/* Applies to all revisions <= r2p1 */
+	mov	x1, #0x21
+	b	cpu_rev_var_ls
+endfunc check_errata_2768515
+
 	/* ----------------------------------------------------
 	 * HW will do the cache maintenance while powering down
 	 * ----------------------------------------------------
@@ -307,6 +331,12 @@ func cortex_x2_core_pwr_dwn
 	mrs	x0, CORTEX_X2_CPUPWRCTLR_EL1
 	orr	x0, x0, #CORTEX_X2_CPUPWRCTLR_EL1_CORE_PWRDN_BIT
 	msr	CORTEX_X2_CPUPWRCTLR_EL1, x0
+#if ERRATA_X2_2768515
+	mov	x15, x30
+	bl	cpu_get_rev_var
+	bl	errata_x2_2768515_wa
+	mov	x30, x15
+#endif /* ERRATA_X2_2768515 */
 	isb
 	ret
 endfunc cortex_x2_core_pwr_dwn
@@ -333,6 +363,7 @@ func cortex_x2_errata_report
 	report_errata ERRATA_X2_2147715, cortex_x2, 2147715
 	report_errata ERRATA_X2_2216384, cortex_x2, 2216384
 	report_errata ERRATA_X2_2371105, cortex_x2, 2371105
+	report_errata ERRATA_X2_2768515, cortex_x2, 2768515
 	report_errata WORKAROUND_CVE_2022_23960, cortex_x2, cve_2022_23960
 	report_errata ERRATA_DSU_2313941, cortex_x2, dsu_2313941
 
diff --git a/lib/cpus/cpu-ops.mk b/lib/cpus/cpu-ops.mk
index 3db86dd22..527a82f28 100644
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@@ -660,6 +660,11 @@ ERRATA_X2_2147715	?=0
 # to revision r0p0, r1p0 and r2p0 of the Cortex-X2 cpu and is fixed in r2p1.
 ERRATA_X2_2371105	?=0
 
+# Flag to apply erratum 2768515 workaround during power down. This erratum
+# applies to revision r0p0, r1p0, r2p0 and r2p1 of the Cortex-X2 cpu and is
+# still open.
+ERRATA_X2_2768515	?=0
+
 # Flag to apply erratum 2313909 workaround on powerdown. This erratum applies
 # to revisions r0p0 and r1p0 of the Cortex-X3 cpu, it is fixed in r1p1.
 ERRATA_X3_2313909	?=0
@@ -1297,6 +1302,10 @@ $(eval $(call add_define,ERRATA_X2_2147715))
 $(eval $(call assert_boolean,ERRATA_X2_2371105))
 $(eval $(call add_define,ERRATA_X2_2371105))
 
+# Process ERRATA_X2_2768515 flag
+$(eval $(call assert_boolean,ERRATA_X2_2768515))
+$(eval $(call add_define,ERRATA_X2_2768515))
+
 # Process ERRATA_X3_2313909 flag
 $(eval $(call assert_boolean,ERRATA_X3_2313909))
 $(eval $(call add_define,ERRATA_X3_2313909))