Check presence of fix for errata 843419 in Cortex-A53

A fix for errata 843419 may be available in revision r0p4 of the
Cortex-A53 processor. The presence of the fix is determined by checking
bit 8 in the REVIDR register.

If the fix is present we report ERRATA_NOT_APPLIES which silences the
erroneous 'missing workaround' warning.

Change-Id: Ibd2a478df3e2a6325442a6a48a0bb0259dcfc1d7
Signed-off-by: Jonathan Wright <jonathan.wright@arm.com>

include/lib/cpus/aarch64/cpu_macros.S

@@ -230,6 +230,7 @@ CPU_OPS_SIZE = .
 
 	/* Check whether errata applies */
 	mov	x0, \_rev_var
+	/* Shall clobber: x0-x7 */
 	bl	check_errata_\_id
 
 	.ifeq \_chosen

lib/cpus/aarch64/cortex_a53.S

 /*
- * Copyright (c) 2014-2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -9,6 +9,7 @@
 #include <cortex_a53.h>
 #include <cpu_macros.S>
 #include <debug.h>
+#include <errata_report.h>
 #include <plat_macros.S>
 
 #if A53_DISABLE_NON_TEMPORAL_HINT
@@ -154,8 +155,22 @@ endfunc check_errata_835769
  * This workaround is statically enabled at build time.
  */
 func check_errata_843419
-	mov	x1, #0x04
-	b	cpu_rev_var_ls
+	mov	x1, #ERRATA_APPLIES
+	mov	x2, #ERRATA_NOT_APPLIES
+	cmp	x0, #0x04
+	csel	x0, x1, x2, ls
+	/*
+	 * Fix potentially available for revision r0p4.
+	 * If r0p4 check for fix in REVIDR, else exit.
+	 */
+	b.ne	exit_check_errata_843419
+	/* Load REVIDR. */
+	mrs	x3, revidr_el1
+	/* If REVIDR[8] is set (fix exists) set ERRATA_NOT_APPLIES, else exit. */
+	tbz	x3, #8, exit_check_errata_843419
+	mov	x0, x2
+exit_check_errata_843419:
+	ret
 endfunc check_errata_843419
 
 	/* -------------------------------------------------

lib/cpus/aarch64/cpu_helpers.S

@@ -198,6 +198,8 @@ endfunc cpu_get_rev_var
  * Compare the CPU's revision-variant (x0) with a given value (x1), for errata
  * application purposes. If the revision-variant is less than or same as a given
  * value, indicates that errata applies; otherwise not.
+ *
+ * Shall clobber: x0-x3
  */
 	.globl	cpu_rev_var_ls
 func cpu_rev_var_ls
@@ -212,6 +214,8 @@ endfunc cpu_rev_var_ls
  * Compare the CPU's revision-variant (x0) with a given value (x1), for errata
  * application purposes. If the revision-variant is higher than or same as a
  * given value, indicates that errata applies; otherwise not.
+ *
+ * Shall clobber: x0-x3
  */
 	.globl	cpu_rev_var_hs
 func cpu_rev_var_hs