Workaround for Cortex A76 erratum 1791580

Cortex A76 erratum 1791580 is a Cat B erratum present in earlier
revisions of the Cortex A76. The workaround is to set a bit in the
implementation defined CPUACTLR2 register, which forces atomic store
operations to write-back memory to be performed in the L1 data cache.

This errata is explained in this SDEN:
https://static.docs.arm.com/sden885749/g/Arm_Cortex_A76_MP052_Software_Developer_Errata_Notice_v20.pdf

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: Iefd58159b3f2e2286138993317b98e57dc361925

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

@@ -227,6 +227,9 @@ For Cortex-A76, the following errata build flags are defined :
 -  ``ERRATA_A76_1275112``: This applies errata 1275112 workaround to Cortex-A76
    CPU. This needs to be enabled only for revision <= r3p0 of the CPU.
 
+-  ``ERRATA_A76_1791580``: This applies errata 1791580 workaround to Cortex-A76
+   CPU. This needs to be enabled only for revision <= r4p0 of the CPU.
+
 For Cortex-A78, the following errata build flags are defined :
 
 -  ``ERRATA_A78_1688305``: This applies errata 1688305 workaround to Cortex-A78

include/lib/cpus/aarch64/cortex_a76.h

 /*
- * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -32,6 +32,8 @@
 
 #define CORTEX_A76_CPUACTLR2_EL1	S3_0_C15_C1_1
 
+#define CORTEX_A76_CPUACTLR2_EL1_BIT_2	(ULL(1) << 2)
+
 #define CORTEX_A76_CPUACTLR2_EL1_DISABLE_LOAD_PASS_STORE	(ULL(1) << 16)
 
 #define CORTEX_A76_CPUACTLR3_EL1	S3_0_C15_C1_2

lib/cpus/aarch64/cortex_a76.S

@@ -392,6 +392,33 @@ func check_errata_1286807
 #endif
 endfunc check_errata_1286807
 
+	/* --------------------------------------------------
+	 * Errata workaround for Cortex A76 Errata #1791580.
+	 * This applies to revisions <= r4p0 of Cortex A76.
+	 * Inputs:
+	 * x0: variant[4:7] and revision[0:3] of current cpu.
+	 * Shall clobber: x0-x17
+	 * --------------------------------------------------
+	 */
+func errata_a76_1791580_wa
+	/* Compare x0 against revision r4p0 */
+	mov	x17, x30
+	bl	check_errata_1791580
+	cbz	x0, 1f
+	mrs	x1, CORTEX_A76_CPUACTLR2_EL1
+	orr	x1, x1, CORTEX_A76_CPUACTLR2_EL1_BIT_2
+	msr	CORTEX_A76_CPUACTLR2_EL1, x1
+	isb
+1:
+	ret	x17
+endfunc errata_a76_1791580_wa
+
+func check_errata_1791580
+	/* Applies to everything <=r4p0. */
+	mov	x1, #0x40
+	b	cpu_rev_var_ls
+endfunc check_errata_1791580
+
 func check_errata_cve_2018_3639
 #if WORKAROUND_CVE_2018_3639
 	mov	x0, #ERRATA_APPLIES
@@ -449,6 +476,11 @@ func cortex_a76_reset_func
 	bl	errata_a76_1262888_wa
 #endif
 
+#if ERRATA_A76_1791580
+	mov	x0, x18
+	bl	errata_a76_1791580_wa
+#endif
+
 #if WORKAROUND_CVE_2018_3639
 	/* If the PE implements SSBS, we don't need the dynamic workaround */
 	mrs	x0, id_aa64pfr1_el1
@@ -529,6 +561,7 @@ func cortex_a76_errata_report
 	report_errata ERRATA_A76_1262888, cortex_a76, 1262888
 	report_errata ERRATA_A76_1275112, cortex_a76, 1275112
 	report_errata ERRATA_A76_1286807, cortex_a76, 1286807
+	report_errata ERRATA_A76_1791580, cortex_a76, 1791580
 	report_errata WORKAROUND_CVE_2018_3639, cortex_a76, cve_2018_3639
 	report_errata ERRATA_DSU_798953, cortex_a76, dsu_798953
 	report_errata ERRATA_DSU_936184, cortex_a76, dsu_936184

lib/cpus/cpu-ops.mk

@@ -250,6 +250,10 @@ ERRATA_A76_1275112	?=0
 # only to revision <= r3p0 of the Cortex A76 cpu.
 ERRATA_A76_1286807	?=0
 
+# Flag to apply erratum 1791580 workaround during reset. This erratum applies
+# only to revision <= r4p0 of the Cortex A76 cpu.
+ERRATA_A76_1791580	?=0
+
 # Flag to apply erratum 1688305 workaround during reset. This erratum applies
 # to revisions r0p0 - r1p0 of the A78 cpu.
 ERRATA_A78_1688305	?=0
@@ -487,6 +491,10 @@ $(eval $(call add_define,ERRATA_A76_1275112))
 $(eval $(call assert_boolean,ERRATA_A76_1286807))
 $(eval $(call add_define,ERRATA_A76_1286807))
 
+# Process ERRATA_A76_1791580 flag
+$(eval $(call assert_boolean,ERRATA_A76_1791580))
+$(eval $(call add_define,ERRATA_A76_1791580))
+
 # Process ERRATA_A78_1688305 flag
 $(eval $(call assert_boolean,ERRATA_A78_1688305))
 $(eval $(call add_define,ERRATA_A78_1688305))