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Subject[RFC Patch v1 36/55] ARC: ARCompact 2 levels IRQ (high/low priority) Handling
Date
From: Vineet Gupta <vgupta@synopsys.com>

There is a bit of hack/kludge right now where we disable preemption if a
L2 (High prio) IRQ is taken while L1 (Low prio) is active.

Need to revisit this

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
arch/arc/Kconfig | 17 ++++++
arch/arc/include/asm/entry.h | 95 +++++++++++++++++++++++++++++++
arch/arc/include/asm/irqflags.h | 6 ++-
arch/arc/kernel/entry.S | 117 +++++++++++++++++++++++++++++++++++++++
arch/arc/kernel/irq.c | 104 ++++++++++++++++++++++++++++++++++
arch/arc/plat-arcfpga/Kconfig | 13 ++++
6 files changed, 351 insertions(+), 1 deletions(-)

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 4557c8d..e096545 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -210,6 +210,23 @@ config ARC_PAGE_SIZE_4K

endchoice

+config ARC_COMPACT_IRQ_LEVELS
+ bool "ARCompact IRQ Priorities: High(2)/Low(1)"
+ default n
+
+if ARC_COMPACT_IRQ_LEVELS
+
+config ARC_IRQ3_LV2
+ bool
+
+config ARC_IRQ5_LV2
+ bool
+
+config ARC_IRQ6_LV2
+ bool
+
+endif
+
config ARC_FPU_SAVE_RESTORE
bool "Enable FPU state persistence across context switch"
default n
diff --git a/arch/arc/include/asm/entry.h b/arch/arc/include/asm/entry.h
index 6113e1a..43dbf6f 100644
--- a/arch/arc/include/asm/entry.h
+++ b/arch/arc/include/asm/entry.h
@@ -5,6 +5,12 @@
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
+ * Vineetg: March 2009 (Supporting 2 levels of Interrupts)
+ * Stack switching code can no longer reliably rely on the fact that
+ * if we are NOT in user mode, stack is switched to kernel mode.
+ * e.g. L2 IRQ interrupted a L1 ISR which had not yet completed
+ * it's prologue including stack switching from user mode
+ *
* Vineetg: Aug 28th 2008: Bug #94984
* -Zero Overhead Loop Context shd be cleared when entering IRQ/EXcp/Trap
* Normally CPU does this automatically, however when doing FAKE rtie,
@@ -233,6 +239,33 @@
* assume SP is kernel mode SP. _NO_ need to do any stack switching
*/

+#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
+ /* However....
+ * If Level 2 Interrupts enabled, we may end up with a corner case:
+ * 1. User Task executing
+ * 2. L1 IRQ taken, ISR starts (CPU auto-switched to KERNEL mode)
+ * 3. But before it could switch SP from USER to KERNEL stack
+ * a L2 IRQ "Interrupts" L1
+ * Thay way although L2 IRQ happened in Kernel mode, stack is still
+ * not switched.
+ * To handle this, we may need to switch stack even if in kernel mode
+ * provided SP has values in range of USER mode stack ( < 0x7000_0000 )
+ */
+ brlo sp, VMALLOC_START, 88f
+
+ /* TODO: vineetg:
+ * We need to be a bit more cautious here. What if a kernel bug in
+ * L1 ISR, caused SP to go whaco (some small value which looks like
+ * USER stk) and then we take L2 ISR.
+ * Above brlo alone would treat it as a valid L1-L2 sceanrio
+ * instead of shouting alound
+ * The only feasible way is to make sure this L2 happened in
+ * L1 prelogue ONLY i.e. ilink2 is less than a pre-set marker in
+ * L1 ISR before it switches stack
+ */
+
+#endif
+
/* Save Pre Intr/Exception KERNEL MODE SP on kernel stack
* safe-keeping not really needed, but it keeps the epilogue code
* (SP restore) simpler/uniform.
@@ -463,6 +496,42 @@
sub sp, sp, 4
.endm

+.macro SAVE_ALL_INT2
+
+ /* TODO-vineetg: SMP we can't use global nor can we use
+ * SCRATCH0 as we do for int1 because while int1 is using
+ * it, int2 can come
+ */
+ /* retsore original r9 , saved in sys_saved_r9 */
+ ld r9, [@int2_saved_reg]
+
+ /* now we are ready to save the remaining context :) */
+ st -2, [sp, 8] /* orig_r8, -2 for interrupt level 2 */
+ st 0, [sp, 4] /* orig_r0 , N/A for IRQ */
+ SAVE_CALLER_SAVED
+ st.a r26, [sp, -4] /* gp */
+ st.a fp, [sp, -4]
+ st.a blink, [sp, -4]
+ st.a ilink2, [sp, -4]
+ lr r9, [status32_l2]
+ st.a r9, [sp, -4]
+ st.a lp_count, [sp, -4]
+ lr r9, [lp_end]
+ st.a r9, [sp, -4]
+ lr r9, [lp_start]
+ st.a r9, [sp, -4]
+ lr r9, [bta_l2]
+ st.a r9, [sp, -4]
+
+#ifdef PT_REGS_CANARY
+ mov r9, 0xdeadbee2
+ st r9, [sp, -4]
+#endif
+
+ /* move up by 1 word to "create" pt_regs->"stack_place_holder" */
+ sub sp, sp, 4
+.endm
+
/*--------------------------------------------------------------
* Restore all registers used by interrupt handlers.
*
@@ -497,6 +566,32 @@
/* orig_r0 and orig_r8 skipped automatically */
.endm

+.macro RESTORE_ALL_INT2
+ add sp, sp, 4 /* hop over unused "pt_regs->stack_place_holder" */
+
+ ld.ab r9, [sp, 4]
+ sr r9, [bta_l2]
+ ld.ab r9, [sp, 4]
+ sr r9, [lp_start]
+ ld.ab r9, [sp, 4]
+ sr r9, [lp_end]
+ ld.ab r9, [sp, 4]
+ mov lp_count, r9
+ ld.ab r9, [sp, 4]
+ sr r9, [status32_l2]
+ ld.ab r9, [sp, 4]
+ mov ilink2, r9
+ ld.ab blink, [sp, 4]
+ ld.ab fp, [sp, 4]
+ ld.ab r26, [sp, 4] /* gp */
+ RESTORE_CALLER_SAVED
+
+ ld sp, [sp] /* restore original sp */
+ /* orig_r0 and orig_r8 skipped automatically */
+
+.endm
+
+
/* Get CPU-ID of this core */
.macro GET_CPU_ID reg
lr \reg, [identity]
diff --git a/arch/arc/include/asm/irqflags.h b/arch/arc/include/asm/irqflags.h
index 752e55d..cc8312d 100644
--- a/arch/arc/include/asm/irqflags.h
+++ b/arch/arc/include/asm/irqflags.h
@@ -95,7 +95,11 @@ static inline long arch_local_save_flags(void)
*/
static inline int arch_irqs_disabled_flags(unsigned long flags)
{
- return !(flags & (STATUS_E1_MASK));
+ return !(flags & (STATUS_E1_MASK
+#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
+ | STATUS_E2_MASK
+#endif
+ ));
}

static inline int arch_irqs_disabled(void)
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 93cde5e..13a0052 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -36,6 +36,8 @@
* exception. Thus FAKE RTIE needed in low level Priv-Violation handler.
* Instr Error could also cause similar scenario, so same there as well.
*
+ * Vineetg: March 2009 (Supporting 2 levels of Interrupts)
+ *
* Vineetg: Aug 28th 2008: Bug #94984
* -Zero Overhead Loop Context shd be cleared when entering IRQ/EXcp/Trap
* Normally CPU does this automatically, however when doing FAKE rtie,
@@ -101,13 +103,25 @@ VECTOR mem_service ; 0x8, Mem exception (0x1)
VECTOR instr_service ; 0x10, Instrn Error (0x2)

; ******************** Device ISRs **********************
+#ifdef CONFIG_ARC_IRQ3_LV2
+VECTOR handle_interrupt_level2
+#else
VECTOR handle_interrupt_level1
+#endif

VECTOR handle_interrupt_level1

+#ifdef CONFIG_ARC_IRQ5_LV2
+VECTOR handle_interrupt_level2
+#else
VECTOR handle_interrupt_level1
+#endif

+#ifdef CONFIG_ARC_IRQ6_LV2
+VECTOR handle_interrupt_level2
+#else
VECTOR handle_interrupt_level1
+#endif

.rept 25
VECTOR handle_interrupt_level1 ; Other devices
@@ -144,6 +158,17 @@ VECTOR reserved ; Reserved Exceptions
int1_saved_reg:
.zero 4

+/* Each Interrupt level needs it's own scratch */
+#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
+
+ .section .data ; NOT .global
+ .type int2_saved_reg, @object
+ .size int2_saved_reg, 4
+int2_saved_reg:
+ .zero 4
+
+#endif
+
; ---------------------------------------------
.section .text, "ax",@progbits

@@ -157,6 +182,55 @@ reserved: ; processor restart

;##################### Interrupt Handling ##############################

+#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
+; ---------------------------------------------
+; Level 2 ISR: Can interrupt a Level 1 ISR
+; ---------------------------------------------
+ARC_ENTRY handle_interrupt_level2
+
+ ; TODO-vineetg for SMP this wont work
+ ; free up r9 as scratchpad
+ st r9, [@int2_saved_reg]
+
+ ;Which mode (user/kernel) was the system in when intr occured
+ lr r9, [status32_l2]
+
+ SWITCH_TO_KERNEL_STK
+ SAVE_ALL_INT2
+
+ ;------------------------------------------------------
+ ; if L2 IRQ interrupted a L1 ISR, disable preemption
+ ;------------------------------------------------------
+
+ 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]
+ add r9, r9, 1
+ st r9, [r10, THREAD_INFO_PREEMPT_COUNT]
+
+1:
+ ;------------------------------------------------------
+ ; setup params for Linux common ISR and invoke it
+ ;------------------------------------------------------
+ lr r0, [icause2]
+ and r0, r0, 0x1f
+
+ bl.d @arch_do_IRQ
+ mov r1, sp
+
+ mov r8,0x2
+ sr r8, [AUX_IRQ_LV12] ; clear bit in Sticky Status Reg
+
+ b ret_from_exception
+
+ARC_EXIT handle_interrupt_level2
+
+#endif
+
; ---------------------------------------------
; Level 1 ISR
; ---------------------------------------------
@@ -625,6 +699,49 @@ restore_regs :

not_exception:

+#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
+
+ bbit0 r10, STATUS_A2_BIT, not_level2_interrupt
+
+ ;------------------------------------------------------------------
+ ; if L2 IRQ interrupted a L1 ISR, we'd disbaled preemption earlier
+ ; so that sched doesnt move to new task, causing L1 to be delayed
+ ; undeterministically. Now that we've achieved that, lets reset
+ ; things to what they were, before returning from L2 context
+ ;----------------------------------------------------------------
+
+ ld r9, [sp, PT_orig_r8] ; get orig_r8 to make sure it is
+ brne r9, -2, 149f ; infact a L2 ISR ret path
+
+ ld r9, [sp, PT_status32] ; get statu32_l2 (saved in pt_regs)
+ bbit0 r9, STATUS_A1_BIT, 149f ; L1 not active when L2 IRQ, so normal
+
+ ; A1 is set in status32_l2
+ ; decrement thread_info->preempt_count (re-enable preemption)
+ GET_CURR_THR_INFO_FROM_SP r10
+ ld r9, [r10, THREAD_INFO_PREEMPT_COUNT]
+
+ ; paranoid check, given A1 was active when A2 happened, preempt count
+ ; must not be 0 beccause we would have incremented it.
+ ; If this does happen we simply HALT as it means a BUG !!!
+ cmp r9, 0
+ bnz 2f
+ flag 1
+
+2:
+ sub r9, r9, 1
+ st r9, [r10, THREAD_INFO_PREEMPT_COUNT]
+
+149:
+ ;return from level 2
+ RESTORE_ALL_INT2
+debug_marker_l2:
+ rtie
+
+not_level2_interrupt:
+
+#endif
+
bbit0 r10, STATUS_A1_BIT, not_level1_interrupt

;return from level 1
diff --git a/arch/arc/kernel/irq.c b/arch/arc/kernel/irq.c
index 03a125c..afde5a7 100644
--- a/arch/arc/kernel/irq.c
+++ b/arch/arc/kernel/irq.c
@@ -21,6 +21,7 @@
* what it does ?
* -setup Vector Table Base Reg - in case Linux not linked at 0x8000_0000
* -Disable all IRQs (on CPU side)
+ * -Optionally, setup the High priority Interrupts as Level 2 IRQs
*/
void __init arc_init_IRQ(void)
{
@@ -30,6 +31,24 @@ void __init arc_init_IRQ(void)

/* Disable all IRQs: enable them as devices request */
write_aux_reg(AUX_IENABLE, 0);
+
+ /* setup any high priority Interrupts (Level2 in ARCompact jargon) */
+#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
+#ifdef CONFIG_ARC_IRQ3_LV2
+ level_mask |= (1 << 3);
+#endif
+#ifdef CONFIG_ARC_IRQ5_LV2
+ level_mask |= (1 << 5);
+#endif
+#ifdef CONFIG_ARC_IRQ6_LV2
+ level_mask |= (1 << 6);
+#endif
+
+ if (level_mask) {
+ pr_info("Level-2 interrupts bitset %x\n", level_mask);
+ write_aux_reg(AUX_IRQ_LEV, level_mask);
+ }
+#endif
}

/*
@@ -87,6 +106,90 @@ int __init get_hw_config_num_irq(void)
return 0;
}

+/*
+ * arch_local_irq_enable - Enable interrupts.
+ *
+ * 1. Explicitly called to re-enable interrupts
+ * 2. Implicitly called from spin_unlock_irq, write_unlock_irq etc
+ * which maybe in hard ISR itself
+ *
+ * Semantics of this function change depending on where it is called from:
+ *
+ * -If called from hard-ISR, it must not invert interrupt priorities
+ * e.g. suppose TIMER is high priority (Level 2) IRQ
+ * Time hard-ISR, timer_interrupt( ) calls spin_unlock_irq several times.
+ * Here local_irq_enable( ) shd not re-enable lower priority interrupts
+ * -If called from soft-ISR, it must re-enable all interrupts
+ * soft ISR are low prioity jobs which can be very slow, thus all IRQs
+ * must be enabled while they run.
+ * Now hardware context wise we may still be in L2 ISR (not done rtie)
+ * still we must re-enable both L1 and L2 IRQs
+ * Another twist is prev scenario with flow being
+ * L1 ISR ==> interrupted by L2 ISR ==> L2 soft ISR
+ * here we must not re-enable Ll as prev Ll Interrupt's h/w context will get
+ * over-written (this is deficiency in ARC700 Interrupt mechanism)
+ */
+
+#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS /* Complex version for 2 IRQ levels */
+
+void arch_local_irq_enable(void)
+{
+
+ unsigned long flags;
+ flags = arch_local_save_flags();
+
+ /* Allow both L1 and L2 at the onset */
+ flags |= (STATUS_E1_MASK | STATUS_E2_MASK);
+
+ /* Called from hard ISR (between irq_enter and irq_exit) */
+ if (in_irq()) {
+
+ /* If in L2 ISR, don't re-enable any further IRQs as this can
+ * cause IRQ priorities to get upside down. e.g. it could allow
+ * L1 be taken while in L2 hard ISR which is wrong not only in
+ * theory, it can also cause the dreaded L1-L2-L1 scenario
+ */
+ if (flags & STATUS_A2_MASK)
+ flags &= ~(STATUS_E1_MASK | STATUS_E2_MASK);
+
+ /* Even if in L1 ISR, allowe Higher prio L2 IRQs */
+ else if (flags & STATUS_A1_MASK)
+ flags &= ~(STATUS_E1_MASK);
+ }
+
+ /* called from soft IRQ, ideally we want to re-enable all levels */
+
+ else if (in_softirq()) {
+
+ /* However if this is case of L1 interrupted by L2,
+ * re-enabling both may cause whaco L1-L2-L1 scenario
+ * because ARC700 allows level 1 to interrupt an active L2 ISR
+ * Thus we disable both
+ * However some code, executing in soft ISR wants some IRQs
+ * to be enabled so we re-enable L2 only
+ *
+ * How do we determine L1 intr by L2
+ * -A2 is set (means in L2 ISR)
+ * -E1 is set in this ISR's pt_regs->status32 which is
+ * saved copy of status32_l2 when l2 ISR happened
+ */
+ struct pt_regs *pt = get_irq_regs();
+ if ((flags & STATUS_A2_MASK) && pt &&
+ (pt->status32 & STATUS_A1_MASK)) {
+ /*flags &= ~(STATUS_E1_MASK | STATUS_E2_MASK); */
+ flags &= ~(STATUS_E1_MASK);
+ }
+ }
+
+ arch_local_irq_restore(flags);
+}
+
+#else /* ! CONFIG_ARC_COMPACT_IRQ_LEVELS */
+
+/*
+ * Simpler version for only 1 level of interrupt
+ * Here we only Worry about Level 1 Bits
+ */
void arch_local_irq_enable(void)
{

@@ -104,4 +207,5 @@ void arch_local_irq_enable(void)

arch_local_irq_restore(flags);
}
+#endif
EXPORT_SYMBOL(arch_local_irq_enable);
diff --git a/arch/arc/plat-arcfpga/Kconfig b/arch/arc/plat-arcfpga/Kconfig
index 3b41a0e..3b399ca 100644
--- a/arch/arc/plat-arcfpga/Kconfig
+++ b/arch/arc/plat-arcfpga/Kconfig
@@ -30,4 +30,17 @@ config ARC_SERIAL_BAUD
help
Baud rate for the ARC UART

+# Platform specific IRQ wiring - tied to devices - feeds into ARC arch code
+config ARC_TIMER_LV2
+ bool "High Priority Timer0 IRQ"
+ depends on ARC_COMPACT_IRQ_LEVELS
+ select ARC_IRQ3_LV2
+
+# Timer HAS to be high priority, for any other high priority config
+config ARC_SERIAL_LV2
+ bool "High Priority Serial IRQ"
+ depends on ARC_SERIAL && ARC_TIMER_LV2
+ depends on ARC_COMPACT_IRQ_LEVELS
+ select ARC_IRQ5_LV2
+
endif
--
1.7.4.1


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