[PATCH v2] arch/sparc: Avoid DCTI Couples

From: Babu Moger
Date: Fri Mar 17 2017 - 16:53:02 EST

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Avoid un-intended DCTI Couples. Use of DCTI couples is deprecated.
Also address the "Programming Note" for optimal performance.

Here is the complete text from Oracle SPARC Architecture Specs.

6.3.4.7 DCTI Couples
"A delayed control transfer instruction (DCTI) in the delay slot of
another DCTI is referred to as a âDCTI coupleâ. The use of DCTI couples
is deprecated in the Oracle SPARC Architecture; no new software should
place a DCTI in the delay slot of another DCTI, because on future Oracle
SPARC Architecture implementations DCTI couples may execute either
slowly or differently than the programmer assumes it will.

SPARC V8 and SPARC V9 Compatibility Note
The SPARC V8 architecture left behavior undefined for a DCTI couple. The
SPARC V9 architecture defined behavior in that case, but as of
UltraSPARC Architecture 2005, use of DCTI couples was deprecated.
Software should not expect high performance from DCTI couples, and
performance of DCTI couples should be expected to decline further in
future processors.

Programming Note
As noted in TABLE 6-5 on page 115, an annulled branch-always
(branch-always with a = 1) instruction is not architecturally a DCTI.
However, since not all implementations make that distinction, for
optimal performance, a DCTI should not be placed in the instruction word
immediately following an annulled branch-always instruction (BA,A or
BPA,A)."

Signed-off-by: Babu Moger <babu.moger@xxxxxxxxxx>
Reviewed-by: Rob Gardner <rob.gardner@xxxxxxxxxx>
---
arch/sparc/kernel/head_64.S | 4 ++++
arch/sparc/kernel/misctrap.S | 1 +
arch/sparc/kernel/rtrap_64.S | 1 +
arch/sparc/kernel/spiterrs.S | 1 +
arch/sparc/kernel/sun4v_tlb_miss.S | 1 +
arch/sparc/kernel/urtt_fill.S | 1 +
arch/sparc/kernel/winfixup.S | 2 ++
arch/sparc/lib/NG2memcpy.S | 4 ++++
arch/sparc/lib/NG4memcpy.S | 1 +
arch/sparc/lib/NG4memset.S | 1 +
arch/sparc/lib/NGmemcpy.S | 1 +
11 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/arch/sparc/kernel/head_64.S b/arch/sparc/kernel/head_64.S
index 6aa3da1..4410119 100644
--- a/arch/sparc/kernel/head_64.S
+++ b/arch/sparc/kernel/head_64.S
@@ -96,6 +96,7 @@ sparc64_boot:
andn %g1, PSTATE_AM, %g1
wrpr %g1, 0x0, %pstate
ba,a,pt %xcc, 1f
+ nop

.globl prom_finddev_name, prom_chosen_path, prom_root_node
.globl prom_getprop_name, prom_mmu_name, prom_peer_name
@@ -613,6 +614,7 @@ niagara_tlb_fixup:
nop

ba,a,pt %xcc, 80f
+ nop
niagara4_patch:
call niagara4_patch_copyops
nop
@@ -622,6 +624,7 @@ niagara4_patch:
nop

ba,a,pt %xcc, 80f
+ nop

niagara2_patch:
call niagara2_patch_copyops
@@ -632,6 +635,7 @@ niagara2_patch:
nop

ba,a,pt %xcc, 80f
+ nop

niagara_patch:
call niagara_patch_copyops
diff --git a/arch/sparc/kernel/misctrap.S b/arch/sparc/kernel/misctrap.S
index 34b4933..9276d2f 100644
--- a/arch/sparc/kernel/misctrap.S
+++ b/arch/sparc/kernel/misctrap.S
@@ -82,6 +82,7 @@ do_stdfmna:
call handle_stdfmna
add %sp, PTREGS_OFF, %o0
ba,a,pt %xcc, rtrap
+ nop
.size do_stdfmna,.-do_stdfmna

.type breakpoint_trap,#function
diff --git a/arch/sparc/kernel/rtrap_64.S b/arch/sparc/kernel/rtrap_64.S
index 216948c..709a82e 100644
--- a/arch/sparc/kernel/rtrap_64.S
+++ b/arch/sparc/kernel/rtrap_64.S
@@ -237,6 +237,7 @@ rt_continue: ldx [%sp + PTREGS_OFF + PT_V9_G1], %g1
bne,pt %xcc, user_rtt_fill_32bit
wrpr %g1, %cwp
ba,a,pt %xcc, user_rtt_fill_64bit
+ nop

user_rtt_fill_fixup_dax:
ba,pt %xcc, user_rtt_fill_fixup_common
diff --git a/arch/sparc/kernel/spiterrs.S b/arch/sparc/kernel/spiterrs.S
index 4a73009..d7e5408 100644
--- a/arch/sparc/kernel/spiterrs.S
+++ b/arch/sparc/kernel/spiterrs.S
@@ -86,6 +86,7 @@ __spitfire_cee_trap_continue:
rd %pc, %g7

ba,a,pt %xcc, 2f
+ nop

1: ba,pt %xcc, etrap_irq
rd %pc, %g7
diff --git a/arch/sparc/kernel/sun4v_tlb_miss.S b/arch/sparc/kernel/sun4v_tlb_miss.S
index 6179e19..c19f352 100644
--- a/arch/sparc/kernel/sun4v_tlb_miss.S
+++ b/arch/sparc/kernel/sun4v_tlb_miss.S
@@ -352,6 +352,7 @@ sun4v_mna:
call sun4v_do_mna
add %sp, PTREGS_OFF, %o0
ba,a,pt %xcc, rtrap
+ nop

/* Privileged Action. */
sun4v_privact:
diff --git a/arch/sparc/kernel/urtt_fill.S b/arch/sparc/kernel/urtt_fill.S
index 5604a2b..364af32 100644
--- a/arch/sparc/kernel/urtt_fill.S
+++ b/arch/sparc/kernel/urtt_fill.S
@@ -92,6 +92,7 @@ user_rtt_fill_fixup_common:
call sun4v_data_access_exception
nop
ba,a,pt %xcc, rtrap
+ nop

1: call spitfire_data_access_exception
nop
diff --git a/arch/sparc/kernel/winfixup.S b/arch/sparc/kernel/winfixup.S
index 855019a..1ee173c 100644
--- a/arch/sparc/kernel/winfixup.S
+++ b/arch/sparc/kernel/winfixup.S
@@ -152,6 +152,8 @@ fill_fixup_dax:
call sun4v_data_access_exception
nop
ba,a,pt %xcc, rtrap
+ nop
1: call spitfire_data_access_exception
nop
ba,a,pt %xcc, rtrap
+ nop
diff --git a/arch/sparc/lib/NG2memcpy.S b/arch/sparc/lib/NG2memcpy.S
index c629dbd..64dcd6c 100644
--- a/arch/sparc/lib/NG2memcpy.S
+++ b/arch/sparc/lib/NG2memcpy.S
@@ -326,11 +326,13 @@ FUNC_NAME: /* %o0=dst, %o1=src, %o2=len */
blu 170f
nop
ba,a,pt %xcc, 180f
+ nop

4: /* 32 <= low bits < 48 */
blu 150f
nop
ba,a,pt %xcc, 160f
+ nop
5: /* 0 < low bits < 32 */
blu,a 6f
cmp %g2, 8
@@ -338,6 +340,7 @@ FUNC_NAME: /* %o0=dst, %o1=src, %o2=len */
blu 130f
nop
ba,a,pt %xcc, 140f
+ nop
6: /* 0 < low bits < 16 */
bgeu 120f
nop
@@ -475,6 +478,7 @@ FUNC_NAME: /* %o0=dst, %o1=src, %o2=len */
brz,pt %o2, 85f
sub %o0, %o1, GLOBAL_SPARE
ba,a,pt %XCC, 90f
+ nop

.align 64
75: /* 16 < len <= 64 */
diff --git a/arch/sparc/lib/NG4memcpy.S b/arch/sparc/lib/NG4memcpy.S
index 75bb93b..78ea962 100644
--- a/arch/sparc/lib/NG4memcpy.S
+++ b/arch/sparc/lib/NG4memcpy.S
@@ -530,4 +530,5 @@ FUNC_NAME: /* %o0=dst, %o1=src, %o2=len */
bne,pt %icc, 1b
EX_ST(STORE(stb, %g1, %o0 - 0x01), NG4_retl_o2_plus_1)
ba,a,pt %icc, .Lexit
+ nop
.size FUNC_NAME, .-FUNC_NAME
diff --git a/arch/sparc/lib/NG4memset.S b/arch/sparc/lib/NG4memset.S
index 41da4bd..7c0c81f 100644
--- a/arch/sparc/lib/NG4memset.S
+++ b/arch/sparc/lib/NG4memset.S
@@ -102,4 +102,5 @@ NG4bzero:
bne,pt %icc, 1b
add %o0, 0x30, %o0
ba,a,pt %icc, .Lpostloop
+ nop
.size NG4bzero,.-NG4bzero
diff --git a/arch/sparc/lib/NGmemcpy.S b/arch/sparc/lib/NGmemcpy.S
index d88c4ed..cd654a7 100644
--- a/arch/sparc/lib/NGmemcpy.S
+++ b/arch/sparc/lib/NGmemcpy.S
@@ -394,6 +394,7 @@ FUNC_NAME: /* %i0=dst, %i1=src, %i2=len */
brz,pt %i2, 85f
sub %o0, %i1, %i3
ba,a,pt %XCC, 90f
+ nop

.align 64
70: /* 16 < len <= 64 */
--
1.7.1

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