fix(errata): workaround for Cortex-X2 errata 2017096

Cortex-X2 erratum 2017096 is a Cat B erratum that applies to
revisions r0p0, r1p0 & r2p0. The workaround is to set CPUECLTR_EL1[8]
to 1 which disables store issue prefetching.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN1775100

Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
Change-Id: I3b740aedc95c2394f6b8d1186014d2b2f640ae05

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

@@ -454,6 +454,10 @@ For Cortex-X2, the following errata build flags are defined :
 -  ``ERRATA_X2_2083908``: This applies errata 2083908 workaround to Cortex-X2
    CPU. This needs to be enabled for revision r2p0 of the CPU, it is still open.
 
+-  ``ERRATA_X2_2017096``: This applies errata 2017096 workaround to
+   Cortex-X2 CPU. This needs to be enabled only for revisions r0p0, r1p0 and
+   r2p0 of the CPU, it is fixed in r2p1.
+
 DSU Errata Workarounds
 ----------------------
 

include/lib/cpus/aarch64/cortex_x2.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -13,6 +13,7 @@
  * CPU Extended Control register specific definitions
  ******************************************************************************/
 #define CORTEX_X2_CPUECTLR_EL1					S3_0_C15_C1_4
+#define CORTEX_X2_CPUECTLR_EL1_PFSTIDIS_BIT			(ULL(1) << 8)
 
 /*******************************************************************************
  * CPU Extended Control register 2 specific definitions

lib/cpus/aarch64/cortex_x2.S

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -113,6 +113,34 @@ func check_errata_2083908
 	b	cpu_rev_var_range
 endfunc check_errata_2083908
 
+	/* --------------------------------------------------
+	 * Errata Workaround for Cortex-X2 Errata 2017096.
+	 * This applies only to revisions r0p0, r1p0 and r2p0
+	 * and is fixed in r2p1.
+	 * Inputs:
+	 * x0: variant[4:7] and revision[0:3] of current cpu.
+	 * Shall clobber: x0, x1, x17
+	 * --------------------------------------------------
+	 */
+func errata_x2_2017096_wa
+	/* Compare x0 against revision r0p0 to r2p0 */
+	mov     x17, x30
+	bl      check_errata_2017096
+	cbz     x0, 1f
+	mrs     x1, CORTEX_X2_CPUECTLR_EL1
+	orr     x1, x1, CORTEX_X2_CPUECTLR_EL1_PFSTIDIS_BIT
+	msr     CORTEX_X2_CPUECTLR_EL1, x1
+
+1:
+	ret     x17
+endfunc errata_x2_2017096_wa
+
+func check_errata_2017096
+	/* Applies to r0p0, r1p0, r2p0 */
+	mov     x1, #0x20
+	b       cpu_rev_var_ls
+endfunc check_errata_2017096
+
 	/* ----------------------------------------------------
 	 * HW will do the cache maintenance while powering down
 	 * ----------------------------------------------------
@@ -146,6 +174,7 @@ func cortex_x2_errata_report
 	report_errata ERRATA_X2_2002765, cortex_x2, 2002765
 	report_errata ERRATA_X2_2058056, cortex_x2, 2058056
 	report_errata ERRATA_X2_2083908, cortex_x2, 2083908
+	report_errata ERRATA_X2_2017096, cortex_x2, 2017096
 
 	ldp	x8, x30, [sp], #16
 	ret
@@ -178,6 +207,11 @@ func cortex_x2_reset_func
 	bl	errata_cortex_x2_2083908_wa
 #endif
 
+#if ERRATA_X2_2017096
+	mov	x0, x18
+	bl	errata_x2_2017096_wa
+#endif
+
 	ret x19
 endfunc cortex_x2_reset_func
 

lib/cpus/cpu-ops.mk

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2014-2021, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2014-2022, ARM Limited and Contributors. All rights reserved.
 # Copyright (c) 2020-2021, NVIDIA Corporation. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
@@ -507,6 +507,11 @@ ERRATA_X2_2058056   ?=0
 # to revision r2p0 of the Cortex-X2 cpu and is still open.
 ERRATA_X2_2083908	?=0
 
+# Flag to apply erratum 2017096 workaround during reset. This erratum applies
+# only to revisions r0p0, r1p0 and r2p0 of the Cortex-X2 cpu, it is fixed in
+# r2p1.
+ERRATA_X2_2017096	?=0
+
 # Flag to apply DSU erratum 798953. This erratum applies to DSUs revision r0p0.
 # Applying the workaround results in higher DSU power consumption on idle.
 ERRATA_DSU_798953	?=0
@@ -944,6 +949,10 @@ $(eval $(call add_define,ERRATA_X2_2058056))
 $(eval $(call assert_boolean,ERRATA_X2_2083908))
 $(eval $(call add_define,ERRATA_X2_2083908))
 
+# Process ERRATA_X2_2017096 flag
+$(eval $(call assert_boolean,ERRATA_X2_2017096))
+$(eval $(call add_define,ERRATA_X2_2017096))
+
 # Process ERRATA_DSU_798953 flag
 $(eval $(call assert_boolean,ERRATA_DSU_798953))
 $(eval $(call add_define,ERRATA_DSU_798953))