fix(cpus): workaround for Cortex-A715 erratum 2331818

Cortex-A715 erratum 2331818 is a cat B erratum that applies to
revisions r0p0 and r1p0 and is fixed in r1p1. The workaround is to
set bit[20] of CPUACTLR2_EL1. Setting this bit is expected to have
a negligible performance impact.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN2148827/latest

Change-Id: If3b1ed78b145ab6515cdd41135314350ed556381
Signed-off-by: Bipin Ravi <biprav01@u203721.austin.arm.com>

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

@@ -881,6 +881,10 @@ For Cortex-A520, the following errata build flags are defined :
 
 For Cortex-A715, the following errata build flags are defined :
 
+-  ``ERRATA_A715_2331818``: This applies errata 2331818 workaround to
+   Cortex-A715 CPU. This needs to be enabled for revisions r0p0 and r1p0.
+   It is fixed in r1p1.
+
 -  ``ERRATA_A715_2420947``: This applies errata 2420947 workaround to
    Cortex-A715 CPU. This needs to be enabled only for revision r1p0.
    It is fixed in r1p1.

lib/cpus/aarch64/cortex_a715.S

@@ -26,6 +26,12 @@
 	wa_cve_2022_23960_bhb_vector_table CORTEX_A715_BHB_LOOP_COUNT, cortex_a715
 #endif /* WORKAROUND_CVE_2022_23960 */
 
+workaround_reset_start cortex_a715, ERRATUM(2331818), ERRATA_A715_2331818
+        sysreg_bit_set CORTEX_A715_CPUACTLR2_EL1, BIT(20)
+workaround_reset_end cortex_a715, ERRATUM(2331818)
+
+check_erratum_ls cortex_a715, ERRATUM(2331818), CPU_REV(1, 0)
+
 workaround_reset_start cortex_a715, ERRATUM(2420947), ERRATA_A715_2420947
         sysreg_bit_set CORTEX_A715_CPUACTLR2_EL1, BIT(33)
 workaround_reset_end cortex_a715, ERRATUM(2420947)

lib/cpus/cpu-ops.mk

@@ -911,6 +911,10 @@ CPU_FLAG_LIST += ERRATA_V2_2779510
 # This erratum applies to revisions r0p0, r0p1. Fixed in r0p2.
 CPU_FLAG_LIST += ERRATA_V2_2801372
 
+# Flag to apply erratum 2331818 workaround during reset. This erratum applies
+# to revisions r0p0 and r1p0. It is fixed in r1p1.
+CPU_FLAG_LIST += ERRATA_A715_2331818
+
 # Flag to apply erratum 2420947 workaround during reset. This erratum applies
 # only to revision r1p0. It is fixed in r1p1.
 CPU_FLAG_LIST += ERRATA_A715_2420947