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ARC: [arcompact] entry.S: Document preemption games for L2 intr 

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
hifive-unleashed-5.1
Vineet Gupta 2015-09-06 19:11:12 +05:30
parent 55a2ae775a
commit 5f88808745
1 changed files with 14 additions and 1 deletions
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15
arch/arc/kernel/entry-compact.S
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@ -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]