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

1 files changed, 7 insertions, 4 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: