1 files changed, 79 insertions, 0 deletions
diff --git a/arch/arm/kernel/fiq.c b/arch/arm/kernel/fiq.c
index 6ff7919613d..c07691ef4c0 100644
--- a/arch/arm/kernel/fiq.c
+++ b/arch/arm/kernel/fiq.c
@@ -8,6 +8,8 @@
  *
  *  FIQ support re-written by Russell King to be more generic
  *
+ *  FIQ handler in C supoprt written by Andy Green <andy@openmoko.com>
+ *
  * We now properly support a method by which the FIQ handlers can
  * be stacked onto the vector.  We still do not support sharing
  * the FIQ vector itself.
@@ -124,6 +126,83 @@ void __naked get_fiq_regs(struct pt_regs *regs)
 	: "r" (&regs->ARM_r8), "I" (PSR_I_BIT | PSR_F_BIT | FIQ_MODE));
 }
 
+/* -------- FIQ handler in C ---------
+ *
+ * Major Caveats for using this
+ *  ---------------------------
+ *  *
+ *  * 1) it CANNOT touch any vmalloc()'d memory, only memory
+ *    that was kmalloc()'d.  Static allocations in the monolithic kernel
+ *    are kmalloc()'d so they are okay.  You can touch memory-mapped IO, but
+ *    the pointer for it has to have been stored in kmalloc'd memory.  The
+ *    reason for this is simple: every now and then Linux turns off interrupts
+ *    and reorders the paging tables.  If a FIQ happens during this time, the
+ *    virtual memory space can be partly or entirely disordered or missing.
+ *
+ * 2) Because vmalloc() is used when a module is inserted, THIS FIQ
+ *    ISR HAS TO BE IN THE MONOLITHIC KERNEL, not a module.  But the way
+ *    it is set up, you can all to enable and disable it from your module
+ *    and intercommunicate with it through struct fiq_ipc
+ *    fiq_ipc which you can define in
+ *    asm/archfiq_ipc_type.h.  The reason is the same as above, a
+ *    FIQ could happen while even the ISR is not present in virtual memory
+ *    space due to pagetables being changed at the time.
+ *
+ * 3) You can't call any Linux API code except simple macros
+ *    - understand that FIQ can come in at any time, no matter what
+ *      state of undress the kernel may privately be in, thinking it
+ *      locked the door by turning off interrupts... FIQ is an
+ *      unstoppable monster force (which is its value)
+ *    - they are not vmalloc()'d memory safe
+ *    - they might do crazy stuff like sleep: FIQ pisses fire and
+ *      is not interested in 'sleep' that the weak seem to need
+ *    - calling APIs from FIQ can re-enter un-renterable things
+ *    - summary: you cannot interoperate with linux APIs directly in the FIQ ISR
+ *
+ * If you follow these rules, it is fantastic, an extremely powerful, solid,
+ * genuine hard realtime feature.
+ */
+
+static void (*current_fiq_c_isr)(void);
+#define FIQ_C_ISR_STACK_SIZE 	256
+
+static void __attribute__((naked)) __jump_to_isr(void)
+{
+	asm __volatile__ ("mov pc, r8");
+}
+
+
+static void __attribute__((naked)) __actual_isr(void)
+{
+	asm __volatile__ (
+		"stmdb	sp!, {r0-r12, lr};"
+		"mov     fp, sp;"
+	);
+
+	current_fiq_c_isr();
+
+	asm __volatile__ (
+		"ldmia	sp!, {r0-r12, lr};"
+		"subs	pc, lr, #4;"
+	);
+}
+
+void set_fiq_c_handler(void (*isr)(void))
+{
+	struct pt_regs regs;
+
+	memset(&regs, 0, sizeof(regs));
+	regs.ARM_r8 = (unsigned long) __actual_isr;
+	regs.ARM_sp = 0xffff001c + FIQ_C_ISR_STACK_SIZE;
+
+	set_fiq_handler(__jump_to_isr, 4);
+
+	current_fiq_c_isr = isr;
+
+	set_fiq_regs(&regs);
+}
+/* -------- FIQ handler in C ---------*/
+
 int claim_fiq(struct fiq_handler *f)
 {
 	int ret = 0;