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Commit 5f888087 authored by Vineet Gupta's avatar Vineet Gupta
Browse files

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



Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent 55a2ae77

arch/arc/kernel/entry-compact.S

+14 −1
Original line number Diff line number Diff line
@@ -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]