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Subject[PATCH] ARCv2: support manual regfile save on interrupts
Date
There's a hardware bug which affects the HSDK platform, triggered by
micro-ops for auto-saving regfile on taken interrupt. The workaround is
to inhibit autosave.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
arch/arc/Kconfig | 8 ++++++
arch/arc/include/asm/entry-arcv2.h | 54 ++++++++++++++++++++++++++++++++++++++
arch/arc/kernel/entry-arcv2.S | 4 ++-
arch/arc/kernel/intc-arcv2.c | 2 ++
arch/arc/plat-hsdk/Kconfig | 1 +
5 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 376366a7db81..7215f52b3413 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -407,6 +407,14 @@ config ARC_HAS_ACCL_REGS
(also referred to as r58:r59). These can also be used by gcc as GPR so
kernel needs to save/restore per process

+config ARC_IRQ_NO_AUTOSAVE
+ bool "Disable hardware autosave regfile on interrupts"
+ default n
+ help
+ On HS cores, taken interrupt auto saves the regfile on stack.
+ This is programmable and can be optionally disabled in which case
+ software INTERRUPT_PROLOGUE/EPILGUE do the needed work
+
endif # ISA_ARCV2

endmenu # "ARC CPU Configuration"
diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h
index 309f4e6721b3..3173d7fa4f72 100644
--- a/arch/arc/include/asm/entry-arcv2.h
+++ b/arch/arc/include/asm/entry-arcv2.h
@@ -17,6 +17,33 @@
;
; Now manually save: r12, sp, fp, gp, r25

+#ifdef CONFIG_ARC_IRQ_NO_AUTOSAVE
+.ifnc \called_from, exception
+ st.as r9, [sp, -10] ; save r9 is right slot
+ sub sp, sp, 12 ; skip JLI, LDI, EI
+
+ PUSH lp_count
+ PUSHAX lp_start
+ PUSHAX lp_end
+ PUSH blink
+
+ PUSH r11
+ PUSH r10
+
+ sub sp, sp, 4 ; skip r9
+
+ PUSH r8
+ PUSH r7
+ PUSH r6
+ PUSH r5
+ PUSH r4
+ PUSH r3
+ PUSH r2
+ PUSH r1
+ PUSH r0
+.endif
+#endif
+
#ifdef CONFIG_ARC_HAS_ACCL_REGS
PUSH r59
PUSH r58
@@ -86,6 +113,33 @@
POP r59
#endif

+#ifdef CONFIG_ARC_IRQ_NO_AUTOSAVE
+.ifnc \called_from, exception
+ POP r0
+ POP r1
+ POP r2
+ POP r3
+ POP r4
+ POP r5
+ POP r6
+ POP r7
+ POP r8
+ POP r9
+ POP r10
+ POP r11
+
+ POP blink
+ POPAX lp_end
+ POPAX lp_start
+
+ POP r9
+ mov lp_count, r9
+
+ add sp, sp, 12 ; skip JLI, LDI, EI
+ ld.as r9, [sp, -10] ; reload r9 which got clobbered
+.endif
+#endif
+
.endm

/*------------------------------------------------------------------------*/
diff --git a/arch/arc/kernel/entry-arcv2.S b/arch/arc/kernel/entry-arcv2.S
index cc558a25b8fa..562089d62d9d 100644
--- a/arch/arc/kernel/entry-arcv2.S
+++ b/arch/arc/kernel/entry-arcv2.S
@@ -209,7 +209,9 @@ restore_regs:
;####### Return from Intr #######

debug_marker_l1:
- bbit1.nt r0, STATUS_DE_BIT, .Lintr_ret_to_delay_slot
+ ; bbit1.nt r0, STATUS_DE_BIT, .Lintr_ret_to_delay_slot
+ btst r0, STATUS_DE_BIT ; Z flag set if bit clear
+ bnz .Lintr_ret_to_delay_slot ; branch if STATUS_DE_BIT set

.Lisr_ret_fast_path:
; Handle special case #1: (Entry via Exception, Return via IRQ)
diff --git a/arch/arc/kernel/intc-arcv2.c b/arch/arc/kernel/intc-arcv2.c
index 067ea362fb3e..cf18b3e5a934 100644
--- a/arch/arc/kernel/intc-arcv2.c
+++ b/arch/arc/kernel/intc-arcv2.c
@@ -49,11 +49,13 @@ void arc_init_IRQ(void)

*(unsigned int *)&ictrl = 0;

+#ifndef CONFIG_ARC_IRQ_NO_AUTOSAVE
ictrl.save_nr_gpr_pairs = 6; /* r0 to r11 (r12 saved manually) */
ictrl.save_blink = 1;
ictrl.save_lp_regs = 1; /* LP_COUNT, LP_START, LP_END */
ictrl.save_u_to_u = 0; /* user ctxt saved on kernel stack */
ictrl.save_idx_regs = 1; /* JLI, LDI, EI */
+#endif

WRITE_AUX(AUX_IRQ_CTRL, ictrl);

diff --git a/arch/arc/plat-hsdk/Kconfig b/arch/arc/plat-hsdk/Kconfig
index f25c085b9874..23e00216e5a5 100644
--- a/arch/arc/plat-hsdk/Kconfig
+++ b/arch/arc/plat-hsdk/Kconfig
@@ -9,6 +9,7 @@ menuconfig ARC_SOC_HSDK
bool "ARC HS Development Kit SOC"
depends on ISA_ARCV2
select ARC_HAS_ACCL_REGS
+ select ARC_IRQ_NO_AUTOSAVE
select CLK_HSDK
select RESET_HSDK
select HAVE_PCI
--
2.7.4
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