Add workaround for errata 855423 of Cortex-A73

Broadcast maintainance operations might not be correctly synchronized
between cores. Set bit 7 of S3_0_C15_C0_2 to prevent this.

Change-Id: I67fb62c0b458d44320ebaedafcb8495ff26c814b
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>

docs/cpu-specific-build-macros.rst

@@ -132,6 +132,11 @@ For Cortex-A72, the following errata build flags are defined :
 -  ``ERRATA_A72_859971``: This applies errata 859971 workaround to Cortex-A72
    CPU. This needs to be enabled only for revision <= r0p3 of the CPU.
 
+For Cortex-A73, the following errata build flags are defined :
+
+-  ``ERRATA_A73_855423``: This applies errata 855423 workaround to Cortex-A73
+   CPU. This needs to be enabled only for revision <= r0p1 of the CPU.
+
 DSU Errata Workarounds
 ----------------------
 

include/lib/cpus/aarch64/cortex_a73.h

@@ -31,4 +31,6 @@
 
 #define CORTEX_A73_IMP_DEF_REG1_DISABLE_LOAD_PASS_STORE	(ULL(1) << 3)
 
+#define CORTEX_A73_IMP_DEF_REG2		S3_0_C15_C0_2
+
 #endif /* CORTEX_A73_H */

lib/cpus/aarch64/cortex_a73.S

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -35,7 +35,47 @@ func cortex_a73_disable_smp
 	ret
 endfunc cortex_a73_disable_smp
 
+	/* ---------------------------------------------------
+	 * Errata Workaround for Cortex A73 Errata #855423.
+	 * This applies only to revision <= r0p1 of Cortex A73.
+	 * Inputs:
+	 * x0: variant[4:7] and revision[0:3] of current cpu.
+	 * Shall clobber: x0-x17
+	 * ---------------------------------------------------
+	 */
+func errata_a73_855423_wa
+	/*
+	 * Compare x0 against revision r0p1
+	 */
+	mov	x17, x30
+	bl	check_errata_855423
+	cbz	x0, 1f
+	mrs	x1, CORTEX_A73_IMP_DEF_REG2
+	orr	x1, x1, #(1 << 7)
+	msr	CORTEX_A73_IMP_DEF_REG2, x1
+	isb
+1:
+	ret	x17
+endfunc errata_a73_855423_wa
+
+func check_errata_855423
+	mov	x1, #0x01
+	b	cpu_rev_var_ls
+endfunc check_errata_855423
+
+	/* -------------------------------------------------
+	 * The CPU Ops reset function for Cortex-A73.
+	 * -------------------------------------------------
+	 */
+
 func cortex_a73_reset_func
+	mov	x19, x30
+	bl	cpu_get_rev_var
+
+#if ERRATA_A73_855423
+	bl	errata_a73_855423_wa
+#endif
+
 #if IMAGE_BL31 && WORKAROUND_CVE_2017_5715
 	cpu_check_csv2	x0, 1f
 	adr	x0, wa_cve_2017_5715_bpiall_vbar
@@ -60,7 +100,7 @@ func cortex_a73_reset_func
 	orr	x0, x0, #CORTEX_A73_CPUECTLR_SMP_BIT
 	msr	CORTEX_A73_CPUECTLR_EL1, x0
 	isb
-	ret
+	ret	x19
 endfunc cortex_a73_reset_func
 
 func cortex_a73_core_pwr_dwn
@@ -160,6 +200,7 @@ func cortex_a73_errata_report
 	 * Report all errata. The revision-variant information is passed to
 	 * checking functions of each errata.
 	 */
+	report_errata ERRATA_A73_855423, cortex_a73, 855423
 	report_errata WORKAROUND_CVE_2017_5715, cortex_a73, cve_2017_5715
 	report_errata WORKAROUND_CVE_2018_3639, cortex_a73, cve_2018_3639
 

lib/cpus/cpu-ops.mk

@@ -119,6 +119,10 @@ ERRATA_A57_859972	?=0
 # only to revision <= r0p3 of the Cortex A72 cpu.
 ERRATA_A72_859971	?=0
 
+# Flag to apply erratum 855423 workaround during reset. This erratum applies
+# only to revision <= r0p1 of the Cortex A73 cpu.
+ERRATA_A73_855423	?=0
+
 # Flag to apply T32 CLREX workaround during reset. This erratum applies
 # only to r0p0 and r1p0 of the Neoverse N1 cpu.
 ERRATA_N1_1043202	?=1
@@ -188,6 +192,10 @@ $(eval $(call add_define,ERRATA_A57_859972))
 $(eval $(call assert_boolean,ERRATA_A72_859971))
 $(eval $(call add_define,ERRATA_A72_859971))
 
+# Process ERRATA_A73_855423 flag
+$(eval $(call assert_boolean,ERRATA_A73_855423))
+$(eval $(call add_define,ERRATA_A73_855423))
+
 # Process ERRATA_N1_1043202 flag
 $(eval $(call assert_boolean,ERRATA_N1_1043202))
 $(eval $(call add_define,ERRATA_N1_1043202))