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
diff --git a/lib/cpus/aarch64/cortex_a53.S b/lib/cpus/aarch64/cortex_a53.S
index e4b94e8..00ceadb 100644
--- 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 @@
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 @@
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
/* ---------------------------------------------
diff --git a/lib/cpus/aarch64/cortex_a57.S b/lib/cpus/aarch64/cortex_a57.S
index 05799d6..8bcb5dd 100644
--- 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 @@
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 @@
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.
diff --git a/lib/cpus/aarch64/cpu_helpers.S b/lib/cpus/aarch64/cpu_helpers.S
index e8a1392..e41d95b 100644
--- 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 @@
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