imx233: add support for nested IRQ

Rewrite IRQ handling to allow nested IRQs: on each IRQ entry, we save the
parameters on the (IRQ) stack and then switch to SVC mode (with its own
stack) and renable interrupts. Make sure interrupt is properly acknowledged
by using the read side-effect (RSE) mode and handle priority levels as well.

Change-Id: I3fd68289b430c56bdd256868939238ff268e42b4

2 files changed, 39 insertions, 11 deletions

diff --git a/firmware/target/arm/imx233/crt0.S b/firmware/target/arm/imx233/crt0.S
index ffc58d56fc..0a71da5d08 100644
--- a/firmware/target/arm/imx233/crt0.S
+++ b/firmware/target/arm/imx233/crt0.S
@@ -132,11 +132,12 @@ remap:
 
     /* Set up stack for FIQ mode */ 
     msr     cpsr_c, #0xd1
-    ldr     sp, =fiq_stack
+    ldr     sp, =irq_stack
 
-    /* Let svc, abort and undefined modes use irq stack */
+    /* Let abort and undefined modes use irq stack, svc uses its own stack
+     * for interrupt processing */
     msr     cpsr_c, #0xd3
-    ldr     sp, =irq_stack
+    ldr     sp, =svc_stack
     msr     cpsr_c, #0xd7
     ldr     sp, =irq_stack
     msr     cpsr_c, #0xdb
@@ -161,11 +162,13 @@ remap:
 1:
     b       1b
 
+/* Cache-align interrupt stacks */
+    .balign    32
 /* 256 words of IRQ stack */
     .space 256*4
 irq_stack:
 
 /* 256 words of FIQ stack */
     .space 256*4
-fiq_stack:
+svc_stack:
 end:
diff --git a/firmware/target/arm/imx233/icoll-imx233.c b/firmware/target/arm/imx233/icoll-imx233.c
index 1c8774ad80..e42e0f3291 100644
--- a/firmware/target/arm/imx233/icoll-imx233.c
+++ b/firmware/target/arm/imx233/icoll-imx233.c
@@ -29,7 +29,7 @@
     extern __attribute__((weak, alias("UIRQ"))) void name(void)
 
 static void UIRQ (void) __attribute__((interrupt ("IRQ")));
-void irq_handler(void) __attribute__((interrupt("IRQ")));
+void irq_handler(void) __attribute__((naked));
 void fiq_handler(void) __attribute__((interrupt("FIQ")));
 
 default_interrupt(INT_USB_CTRL);
@@ -161,17 +161,40 @@ static void UIRQ(void)
         (unsigned int)(HW_ICOLL_VECTOR - (uint32_t)isr_table) / 4);
 }
 
-void irq_handler(void)
+/* return the priority level */
+int _irq_handler(uint32_t vec)
 {
-    HW_ICOLL_VECTOR = HW_ICOLL_VECTOR; /* notify icoll that we entered ISR */
-    int irq_nr = (HW_ICOLL_VECTOR - HW_ICOLL_VBASE) / 4;
+    int irq_nr = (vec - HW_ICOLL_VBASE) / 4;
     if(irq_count[irq_nr]++ > IRQ_STORM_THRESHOLD)
         panicf("IRQ %d: storm detected", irq_nr);
     if(irq_nr == INT_SRC_TIMER(TIMER_TICK))
         do_irq_stat();
-    (*(isr_t *)HW_ICOLL_VECTOR)();
-    /* acknowledge completion of IRQ (all use the same priority 0) */
-    HW_ICOLL_LEVELACK = BV_ICOLL_LEVELACK_IRQLEVELACK__LEVEL0;
+    (*(isr_t *)vec)();
+    /* acknowledge completion of IRQ */
+    return imx233_icoll_get_irq_info(irq_nr).priority;
+}
+
+void irq_handler(void)
+{
+    /* save stuff */
+    asm volatile(
+        "sub    lr, lr, #4               \n" /* Create return address */
+        "stmfd  sp!, { r0-r5, r12, lr }  \n" /* Save what gets clobbered */
+        "ldr    r4, =0x80000000          \n" /* Read HW_ICOLL_VECTOR  */
+        "ldr    r0, [r4]                 \n" /* and notify as side-effect */
+        "mrs    lr, spsr                 \n" /* Save SPSR_irq */
+        "stmfd  sp!, { lr }              \n" /* Push it on the IRQ stack */
+        "msr    cpsr_c, #0x13            \n" /* Switch to SVC mode, enable IRQ */
+        "stmfd  sp!, { lr }              \n" /* Save lr_SVC */
+        "blx    _irq_handler             \n" /* Process IRQ, returns ack level */
+        "ldmfd  sp!, { lr }              \n" /* Restore lr_SVC */
+        "msr    cpsr_c, #0x92            \n" /* Mask IRQ, return to IRQ mode */
+        "ldmfd  sp!, { lr }              \n" /* Pop back SPSR */
+        "msr    spsr_cxsf, lr            \n" /* Restore SPSR_irq */
+        "mov    r3, #1                   \n" /* Compute ack level value */
+        "lsl    r0, r3, r0               \n" /* (1 << ack_lvl) */
+        "str    r0, [r4, #0x10]          \n" /* and write it to HW_ICOLL_LEVELACK */
+        "ldmfd  sp!, { r0-r5, r12, pc }^ \n" /* Restore regs, and RFE */);
 }
 
 void fiq_handler(void)
@@ -220,6 +243,8 @@ void imx233_icoll_set_priority(int src, unsigned prio)
 void imx233_icoll_init(void)
 {
     imx233_reset_block(&HW_ICOLL_CTRL);
+    /* enable read side-effect mode for nested interrupts */
+    BF_SET(ICOLL_CTRL, ARM_RSE_MODE);
     /* disable all interrupts */
     /* priority = 0, disable, disable fiq */
 #if IMX233_SUBTARGET >= 3780