Disable non-temporal hint on Cortex-A53/57

The LDNP/STNP instructions as implemented on Cortex-A53 and Cortex-A57 do not behave in a way most programmers expect, and will most probably result in a significant speed degradation to any code that employs them. The ARMv8-A architecture (see Document ARM DDI 0487A.h, section D3.4.3) allows cores to ignore the non-temporal hint and treat LDNP/STNP as LDP/STP instead. This patch introduces 2 new build flags: A53_DISABLE_NON_TEMPORAL_HINT and A57_DISABLE_NON_TEMPORAL_HINT to enforce this behaviour on Cortex-A53 and Cortex-A57. They are enabled by default. The string printed in debug builds when a specific CPU errata workaround is compiled in but skipped at runtime has been generalised, so that it can be reused for the non-temporal hint use case as well. Change-Id: I3e354f4797fd5d3959872a678e160322b13867a1
2016-01-13 14:57:38 +00:00 · 2016-01-13 14:57:38 +00:00 · 54035fc467
parent dbc807179f
commit 54035fc467
7 changed files with 105 additions and 33 deletions
--- a/8
+++ b/8
@ -1,5 +1,5 @@
 #
-# Copyright (c) 2013-2015, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2013-2016, ARM Limited and Contributors. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are met:
@ -294,9 +294,9 @@ ifneq (${ENABLE_PLAT_COMPAT}, 0)
 include plat/compat/plat_compat.mk
 endif

-# Include the CPU specific operations makefile. By default all CPU errata
-# workarounds and CPU specific optimisations are disabled. This can be
-# overridden by the platform.
+# Include the CPU specific operations makefile, which provides default
+# values for all CPU errata workarounds and CPU specific optimisations.
+# This can be overridden by the platform.
 include lib/cpus/cpu-ops.mk


--- a/docs/cpu-specific-build-macros.md
+++ b/docs/cpu-specific-build-macros.md
@ -26,8 +26,8 @@ by ARM. The errata workarounds are implemented for a particular revision
 or a set of processor revisions. This is checked by reset handler at runtime.
 Each errata workaround is identified by its `ID` as specified in the processor's
 errata notice document. The format of the define used to enable/disable the
-errata is `ERRATA_<Processor name>_<ID>` where the `Processor name`
-is either `A57` for the `Cortex_A57` CPU or `A53` for `Cortex_A53` CPU.
+errata workaround is `ERRATA_<Processor name>_<ID>`, where the `Processor name`
+is for example `A57` for the `Cortex_A57` CPU.

 All workarounds are disabled by default. The platform is reponsible for
 enabling these workarounds according to its requirement by defining the
@ -74,6 +74,19 @@ architecture that can be enabled by the platform as desired.
     sequence. Each Cortex-A57 based platform must make its own decision on
     whether to use the optimization.

+*    `A53_DISABLE_NON_TEMPORAL_HINT`: This flag disables the cache non-temporal
+     hint. The LDNP/STNP instructions as implemented on Cortex-A53 do not behave
+     in a way most programmers expect, and will most probably result in a
+     significant speed degradation to any code that employs them. The ARMv8-A
+     architecture (see ARM DDI 0487A.h, section D3.4.3) allows cores to ignore
+     the non-temporal hint and treat LDNP/STNP as LDP/STP instead. Enabling this
+     flag enforces this behaviour. This needs to be enabled only for revisions
+     <= r0p3 of the CPU and is enabled by default.
+
+*    `A57_DISABLE_NON_TEMPORAL_HINT`: This flag has the same behaviour as
+     `A53_DISABLE_NON_TEMPORAL_HINT` but for Cortex-A57. This needs to be
+     enabled only for revisions <= r1p2 of the CPU and is enabled by default.
+
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

-_Copyright (c) 2014, ARM Limited and Contributors. All rights reserved._
+_Copyright (c) 2014-2016, ARM Limited and Contributors. All rights reserved._
--- a/include/lib/cpus/aarch64/cortex_a57.h
+++ b/include/lib/cpus/aarch64/cortex_a57.h
@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014-2015, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2016, ARM Limited and Contributors. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
@ -61,8 +61,9 @@
 ******************************************************************************/
 #define CPUACTLR_EL1			S3_1_C15_C2_0	/* Instruction def. */

-#define CPUACTLR_NO_ALLOC_WBWA         (1 << 49)
-#define CPUACTLR_DCC_AS_DCCI           (1 << 44)
+#define CPUACTLR_DIS_OVERREAD		(1 << 52)
+#define CPUACTLR_NO_ALLOC_WBWA		(1 << 49)
+#define CPUACTLR_DCC_AS_DCCI		(1 << 44)

 /*******************************************************************************
 * L2 Control register specific definitions.
--- a/lib/cpus/aarch64/cortex_a53.S
+++ b/lib/cpus/aarch64/cortex_a53.S
@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2016, ARM Limited and Contributors. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
@ -86,33 +86,40 @@ apply_826319:
 	ret
 endfunc errata_a53_826319_wa

-	/* --------------------------------------------------
-	 * Errata Workaround for Cortex A53 Errata #836870.
-	 * This applies only to revision <= r0p3 of Cortex A53.
-	 * From r0p4 and onwards, this errata is enabled by
-	 * default.
+	/* ---------------------------------------------------------------------
+	 * Disable the cache non-temporal hint.
+	 *
+	 * This ignores the Transient allocation hint in the MAIR and treats
+	 * allocations the same as non-transient allocation types. As a result,
+	 * the LDNP and STNP instructions in AArch64 behave the same as the
+	 * equivalent LDP and STP instructions.
+	 *
+	 * This is relevant only for revisions <= r0p3 of Cortex-A53.
+	 * From r0p4 and onwards, the bit to disable the hint is enabled by
+	 * default at reset.
+	 *
 	 * Inputs:
 	 * x0: variant[4:7] and revision[0:3] of current cpu.
 	 * Clobbers : x0 - x5
-	 * --------------------------------------------------
+	 * ---------------------------------------------------------------------
 	 */
-func errata_a53_836870_wa
+func a53_disable_non_temporal_hint
 	/*
 	 * Compare x0 against revision r0p3
 	 */
 	cmp	x0, #3
-	b.ls	apply_836870
+	b.ls	disable_hint
 #if DEBUG
 	b	print_revision_warning
 #else
 	ret
 #endif
-apply_836870:
+disable_hint:
 	mrs	x1, CPUACTLR_EL1
 	orr	x1, x1, #CPUACTLR_DTAH
 	msr	CPUACTLR_EL1, x1
 	ret
-endfunc errata_a53_836870_wa
+endfunc a53_disable_non_temporal_hint

 	/* -------------------------------------------------
 	 * The CPU Ops reset function for Cortex-A53.
@ -138,9 +145,9 @@ func cortex_a53_reset_func
 	bl	errata_a53_826319_wa
 #endif

-#if ERRATA_A53_836870
+#if ERRATA_A53_836870 || A53_DISABLE_NON_TEMPORAL_HINT
 	mov	x0, x15
-	bl	errata_a53_836870_wa
+	bl	a53_disable_non_temporal_hint
 #endif

 	/* ---------------------------------------------
--- a/lib/cpus/aarch64/cortex_a57.S
+++ b/lib/cpus/aarch64/cortex_a57.S
@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2016, ARM Limited and Contributors. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
@ -153,6 +153,35 @@ skip_813420:
 	ret
 endfunc errata_a57_813420_wa

+	/* --------------------------------------------------------------------
+	 * Disable the over-read from the LDNP instruction.
+	 *
+	 * This applies to all revisions <= r1p2. The performance degradation
+	 * observed with LDNP/STNP has been fixed on r1p3 and onwards.
+	 *
+	 * Inputs:
+	 * x0: variant[4:7] and revision[0:3] of current cpu.
+	 * Clobbers : x0 - x5, x30
+	 * ---------------------------------------------------------------------
+	 */
+func a57_disable_ldnp_overread
+	/*
+	 * Compare x0 against revision r1p2
+	 */
+	cmp	x0, #0x12
+	b.ls	disable_hint
+#if DEBUG
+	b	print_revision_warning
+#else
+	ret
+#endif
+disable_hint:
+	mrs	x1, CPUACTLR_EL1
+	orr	x1, x1, #CPUACTLR_DIS_OVERREAD
+	msr	CPUACTLR_EL1, x1
+	ret
+endfunc a57_disable_ldnp_overread
+
 	/* -------------------------------------------------
 	 * The CPU Ops reset function for Cortex-A57.
 	 * Clobbers: x0-x5, x15, x19, x30
@ -181,6 +210,11 @@ func cortex_a57_reset_func
 	bl	errata_a57_813420_wa
 #endif

+#if A57_DISABLE_NON_TEMPORAL_HINT
+	mov	x0, x15
+	bl	a57_disable_ldnp_overread
+#endif
+
 	/* ---------------------------------------------
 	 * As a bare minimum enable the SMP bit if it is
 	 * not already set.
--- a/lib/cpus/aarch64/cpu_helpers.S
+++ b/lib/cpus/aarch64/cpu_helpers.S
@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2016, ARM Limited and Contributors. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
@ -205,16 +205,17 @@ error_exit:
 endfunc get_cpu_ops_ptr

 #if DEBUG
-	/*
-	 * This function prints a warning message to the crash console
-	 * if the CPU revision/part number does not match the errata
-	 * workaround enabled in the build.
-	 * Clobber: x30, x0 - x5
-	 */
 .section .rodata.rev_warn_str, "aS"
 rev_warn_str:
-	.asciz "Warning: Skipping Errata workaround for non matching CPU revision number.\n"
+	.asciz "Warning: Skipping CPU specific reset operation for non-matching CPU revision number.\n"

+	/*
+	 * This function prints the above warning message to the crash console.
+	 * It should be called when a CPU specific operation is enabled in the
+	 * build but doesn't apply to this CPU revision/part number.
+	 *
+	 * Clobber: x30, x0 - x5
+	 */
 	.globl	print_revision_warning
 func print_revision_warning
 	mov	x5, x30
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@ -1,5 +1,5 @@
 #
-# Copyright (c) 2014, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2014-2016, ARM Limited and Contributors. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are met:
@ -32,10 +32,26 @@
 # cluster is powered down.
 SKIP_A57_L1_FLUSH_PWR_DWN	?=0

+# Flag to disable the cache non-temporal hint.
+# It is enabled by default.
+A53_DISABLE_NON_TEMPORAL_HINT	?=1
+
+# Flag to disable the cache non-temporal hint.
+# It is enabled by default.
+A57_DISABLE_NON_TEMPORAL_HINT	?=1
+
 # Process SKIP_A57_L1_FLUSH_PWR_DWN flag
 $(eval $(call assert_boolean,SKIP_A57_L1_FLUSH_PWR_DWN))
 $(eval $(call add_define,SKIP_A57_L1_FLUSH_PWR_DWN))

+# Process A53_DISABLE_NON_TEMPORAL_HINT flag
+$(eval $(call assert_boolean,A53_DISABLE_NON_TEMPORAL_HINT))
+$(eval $(call add_define,A53_DISABLE_NON_TEMPORAL_HINT))
+
+# Process A57_DISABLE_NON_TEMPORAL_HINT flag
+$(eval $(call assert_boolean,A57_DISABLE_NON_TEMPORAL_HINT))
+$(eval $(call add_define,A57_DISABLE_NON_TEMPORAL_HINT))
+

 # CPU Errata Build flags. These should be enabled by the
 # platform if the errata needs to be applied.