feat(cpus): workaround for Cortex A78 AE erratum 1941500

Cortex A78 AE erratum 1941500 is a Cat B erratum that applies
to revisions <= r0p1. It is still open.

This erratum is avoided by by setting CPUECTLR_EL1[8] to 1.
There is a small performance cost (<0.5%) for setting this
bit.

SDEN is available at https://developer.arm.com/documentation/SDEN1707912/0900



Change-Id: I2d72666468b146714a0340ba114ccf0f5165b39c
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

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

@@ -283,6 +283,10 @@ For Cortex-A78, the following errata build flags are defined :
 
 For Cortex-A78 AE, the following errata build flags are defined :
 
+- ``ERRATA_A78_AE_1941500`` : This applies errata 1941500 workaround to Cortex-A78
+   AE CPU. This needs to be enabled for revisions r0p0 and r0p1. This erratum is
+   still open.
+
 - ``ERRATA_A78_AE_1951502`` : This applies errata 1951502 workaround to Cortex-A78
   AE CPU. This needs to be enabled for revisions r0p0 and r0p1. This erratum is
   still open.

include/lib/cpus/aarch64/cortex_a78_ae.h

 /*
  * Copyright (c) 2019-2020, ARM Limited. All rights reserved.
+ * Copyright (c) 2021, NVIDIA Corporation. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -11,4 +12,10 @@
 
 #define CORTEX_A78_AE_MIDR U(0x410FD420)
 
+/*******************************************************************************
+ * CPU Extended Control register specific definitions.
+ ******************************************************************************/
+#define CORTEX_A78_AE_CPUECTLR_EL1			CORTEX_A78_CPUECTLR_EL1
+#define CORTEX_A78_AE_CPUECTLR_EL1_BIT_8		CORTEX_A78_CPUECTLR_EL1_BIT_8
+
 #endif /* CORTEX_A78_AE_H */

lib/cpus/aarch64/cortex_a78_ae.S

@@ -17,6 +17,36 @@
 #error "cortex_a78_ae must be compiled with HW_ASSISTED_COHERENCY enabled"
 #endif
 
+/* --------------------------------------------------
+ * Errata Workaround for A78 AE Erratum 1941500.
+ * This applies to revisions r0p0 and r0p1 of A78 AE.
+ * Inputs:
+ * x0: variant[4:7] and revision[0:3] of current cpu.
+ * Shall clobber: x0-x17
+ * --------------------------------------------------
+ */
+func errata_a78_ae_1941500_wa
+	/* Compare x0 against revisions r0p0 - r0p1 */
+	mov	x17, x30
+	bl	check_errata_1941500
+	cbz	x0, 1f
+
+	/* Set bit 8 in ECTLR_EL1 */
+	mrs	x0, CORTEX_A78_AE_CPUECTLR_EL1
+	bic	x0, x0, #CORTEX_A78_AE_CPUECTLR_EL1_BIT_8
+	msr	CORTEX_A78_AE_CPUECTLR_EL1, x0
+	isb
+1:
+	ret	x17
+endfunc errata_a78_ae_1941500_wa
+
+func check_errata_1941500
+	/* Applies to revisions r0p0 and r0p1. */
+	mov	x1, #CPU_REV(0, 0)
+	mov	x2, #CPU_REV(0, 1)
+	b	cpu_rev_var_range
+endfunc check_errata_1941500
+
 /* --------------------------------------------------
  * Errata Workaround for A78 AE Erratum 1951502.
  * This applies to revisions r0p0 and r0p1 of A78 AE.
@@ -78,6 +108,11 @@ func cortex_a78_ae_reset_func
 	bl	cpu_get_rev_var
 	mov	x18, x0
 
+#if ERRATA_A78_AE_1941500
+	mov	x0, x18
+	bl	errata_a78_ae_1941500_wa
+#endif
+
 #if ERRATA_A78_AE_1951502
 	mov	x0, x18
 	bl	errata_a78_ae_1951502_wa
@@ -138,6 +173,7 @@ func cortex_a78_ae_errata_report
 	 * Report all errata. The revision-variant information is passed to
 	 * checking functions of each errata.
 	 */
+	report_errata ERRATA_A78_AE_1941500, cortex_a78_ae, 1941500
 	report_errata ERRATA_A78_AE_1951502, cortex_a78_ae, 1951502
 
 	ldp	x8, x30, [sp], #16

lib/cpus/cpu-ops.mk

@@ -311,6 +311,10 @@ ERRATA_A78_1941498	?=0
 # well but there is no workaround for that revision.
 ERRATA_A78_1951500	?=0
 
+# Flag to apply erratum 1941500 workaround during reset. This erratum applies
+# to revisions r0p0 and r0p1 of the A78 AE cpu. It is still open.
+ERRATA_A78_AE_1941500	?=0
+
 # Flag to apply erratum 1951502 workaround during reset. This erratum applies
 # to revisions r0p0 and r0p1 of the A78 AE cpu. It is still open.
 ERRATA_A78_AE_1951502	?=0
@@ -650,6 +654,10 @@ $(eval $(call add_define,ERRATA_A78_1941498))
 $(eval $(call assert_boolean,ERRATA_A78_1951500))
 $(eval $(call add_define,ERRATA_A78_1951500))
 
+# Process ERRATA_A78_AE_1941500 flag
+$(eval $(call assert_boolean,ERRATA_A78_AE_1941500))
+$(eval $(call add_define,ERRATA_A78_AE_1941500))
+
 # Process ERRATA_A78_AE_1951502 flag
 $(eval $(call assert_boolean,ERRATA_A78_AE_1951502))
 $(eval $(call add_define,ERRATA_A78_AE_1951502))