ARM: 8150/3: fiq: Replace default FIQ handler

This patch introduces a new default FIQ handler that is structured in a
similar way to the existing ARM exception handler and result in the FIQ
being handled by C code running on the SVC stack (despite this code run
in the FIQ handler is subject to severe limitations with respect to
locking making normal interaction with the kernel impossible).

This default handler allows concepts that on x86 would be handled using
NMIs to be realized on ARM.

Credit:

    This patch is a near complete re-write of a patch originally
    provided by Anton Vorontsov. Today only a couple of small fragments
    survive, however without Anton's work to build from this patch would
    not exist. Thanks also to Russell King for spoonfeeding me a variety
    of fixes during the review cycle.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 13 insertions, 4 deletions

diff --git a/arch/arm/kernel/fiq.c b/arch/arm/kernel/fiq.c
index 918875d96d5d..b37752a96652 100644
--- a/arch/arm/kernel/fiq.c
+++ b/arch/arm/kernel/fiq.c
@@ -52,7 +52,8 @@
 		(unsigned)&vector_fiq_offset;		\
 	})
 
-static unsigned long no_fiq_insn;
+static unsigned long dfl_fiq_insn;
+static struct pt_regs dfl_fiq_regs;
 
 /* Default reacquire function
  * - we always relinquish FIQ control
@@ -60,8 +61,15 @@ static unsigned long no_fiq_insn;
  */
 static int fiq_def_op(void *ref, int relinquish)
 {
-	if (!relinquish)
-		set_fiq_handler(&no_fiq_insn, sizeof(no_fiq_insn));
+	if (!relinquish) {
+		/* Restore default handler and registers */
+		local_fiq_disable();
+		set_fiq_regs(&dfl_fiq_regs);
+		set_fiq_handler(&dfl_fiq_insn, sizeof(dfl_fiq_insn));
+		local_fiq_enable();
+
+		/* FIXME: notify irq controller to standard enable FIQs */
+	}
 
 	return 0;
 }
@@ -150,6 +158,7 @@ EXPORT_SYMBOL(disable_fiq);
 void __init init_FIQ(int start)
 {
 	unsigned offset = FIQ_OFFSET;
-	no_fiq_insn = *(unsigned long *)(0xffff0000 + offset);
+	dfl_fiq_insn = *(unsigned long *)(0xffff0000 + offset);
+	get_fiq_regs(&dfl_fiq_regs);
 	fiq_start = start;
 }