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authorVineet Gupta <vgupta@synopsys.com>2015-09-06 19:11:12 +0530
committerVineet Gupta <vgupta@synopsys.com>2015-10-17 17:48:23 +0530
commit5f888087455c5199195c2ba17b91ac7285a33921 (patch)
tree6751413f87bccba6a83e240e867ffe9d37705ed9 /arch/arc
parent55a2ae775ab4fe7aefa736e0fae6b8d4bd8aaab5 (diff)
ARC: [arcompact] entry.S: Document preemption games for L2 intr
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Diffstat (limited to 'arch/arc')
-rw-r--r--arch/arc/kernel/entry-compact.S15
1 files changed, 14 insertions, 1 deletions
diff --git a/arch/arc/kernel/entry-compact.S b/arch/arc/kernel/entry-compact.S
index 15d457b4403a..d9087a1236eb 100644
--- a/arch/arc/kernel/entry-compact.S
+++ b/arch/arc/kernel/entry-compact.S
@@ -175,12 +175,25 @@ ENTRY(handle_interrupt_level2)
;------------------------------------------------------
; if L2 IRQ interrupted a L1 ISR, disable preemption
+ ;
+ ; This is to avoid a potential L1-L2-L1 scenario
+ ; -L1 IRQ taken
+ ; -L2 interrupts L1 (before L1 ISR could run)
+ ; -preemption off IRQ, user task in syscall picked to run
+ ; -RTIE to userspace
+ ; Returns from L2 context fine
+ ; But both L1 and L2 re-enabled, so another L1 can be taken
+ ; while prev L1 is still unserviced
+ ;
;------------------------------------------------------
+ ; L2 interrupting L1 implies both L2 and L1 active
+ ; However both A2 and A1 are NOT set in STATUS32, thus
+ ; need to check STATUS32_L2 to determine if L1 was active
+
ld r9, [sp, PT_status32] ; get statu32_l2 (saved in pt_regs)
bbit0 r9, STATUS_A1_BIT, 1f ; L1 not active when L2 IRQ, so normal
- ; A1 is set in status32_l2
; bump thread_info->preempt_count (Disable preemption)
GET_CURR_THR_INFO_FROM_SP r10
ld r9, [r10, THREAD_INFO_PREEMPT_COUNT]