powerpc: Consolidate ipi message mux and demux

Consolidate the mux and demux of ipi messages into smp.c and call
a new smp_ops callback to actually trigger the ipi.

The powerpc architecture code is optimised for having 4 distinct
ipi triggers, which are mapped to 4 distinct messages (ipi many, ipi
single, scheduler ipi, and enter debugger).  However, several interrupt
controllers only provide a single software triggered interrupt that
can be delivered to each cpu.  To resolve this limitation, each smp_ops
implementation created a per-cpu variable that is manipulated with atomic
bitops.  Since these lines will be contended they are optimialy marked as
shared_aligned and take a full cache line for each cpu.  Distro kernels
may have 2 or 3 of these in their config, each taking per-cpu space
even though at most one will be in use.

This consolidation removes smp_message_recv and replaces the single call
actions cases with direct calls from the common message recognition loop.
The complicated debugger ipi case with its muxed crash handling code is
moved to debug_ipi_action which is now called from the demux code (instead
of the multi-message action calling smp_message_recv).

I put a call to reschedule_action to increase the likelyhood of correctly
merging the anticipated scheduler_ipi() hook coming from the scheduler
tree; that single required call can be inlined later.

The actual message decode is a copy of the old pseries xics code with its
memory barriers and cache line spacing, augmented with a per-cpu unsigned
long based on the book-e doorbell code.  The optional data is set via a
callback from the implementation and is passed to the new cause-ipi hook
along with the logical cpu number.  While currently only the doorbell
implemntation uses this data it should be almost zero cost to retrieve and
pass it -- it adds a single register load for the argument from the same
cache line to which we just completed a store and the register is dead
on return from the call.  I extended the data element from unsigned int
to unsigned long in case some other code wanted to associate a pointer.

The doorbell check_self is replaced by a call to smp_muxed_ipi_resend,
conditioned on the CPU_DBELL feature.  The ifdef guard could be relaxed
to CONFIG_SMP but I left it with BOOKE for now.

Also, the doorbell interrupt vector for book-e was not calling irq_enter
and irq_exit, which throws off cpu accounting and causes code to not
realize it is running in interrupt context.  Add the missing calls.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

3 files changed, 73 insertions, 71 deletions

diff --git a/arch/powerpc/kernel/dbell.c b/arch/powerpc/kernel/dbell.c
index e49b24c84133..2cc451aaaca7 100644
--- a/arch/powerpc/kernel/dbell.c
+++ b/arch/powerpc/kernel/dbell.c
@@ -13,65 +13,35 @@
 #include <linux/kernel.h>
 #include <linux/smp.h>
 #include <linux/threads.h>
-#include <linux/percpu.h>
+#include <linux/hardirq.h>
 
 #include <asm/dbell.h>
 #include <asm/irq_regs.h>
 
 #ifdef CONFIG_SMP
-struct doorbell_cpu_info {
-	unsigned long	messages;	/* current messages bits */
-	unsigned int	tag;		/* tag value */
-};
-
-static DEFINE_PER_CPU(struct doorbell_cpu_info, doorbell_cpu_info);
-
 void doorbell_setup_this_cpu(void)
 {
-	struct doorbell_cpu_info *info = &__get_cpu_var(doorbell_cpu_info);
+	unsigned long tag = mfspr(SPRN_PIR) & 0x3fff;
 
-	info->messages = 0;
-	info->tag = mfspr(SPRN_PIR) & 0x3fff;
+	smp_muxed_ipi_set_data(smp_processor_id(), tag);
 }
 
-void doorbell_message_pass(int cpu, int msg)
+void doorbell_cause_ipi(int cpu, unsigned long data)
 {
-	struct doorbell_cpu_info *info;
-
-	info = &per_cpu(doorbell_cpu_info, cpu);
-	set_bit(msg, &info->messages);
-	ppc_msgsnd(PPC_DBELL, 0, info->tag);
+	ppc_msgsnd(PPC_DBELL, 0, data);
 }
 
 void doorbell_exception(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);
-	struct doorbell_cpu_info *info = &__get_cpu_var(doorbell_cpu_info);
-	int msg;
 
-	/* Warning: regs can be NULL when called from irq enable */
+	irq_enter();
 
-	if (!info->messages || (num_online_cpus() < 2))
-		goto out;
+	smp_ipi_demux();
 
-	for (msg = 0; msg < 4; msg++)
-		if (test_and_clear_bit(msg, &info->messages))
-			smp_message_recv(msg);
-
-out:
+	irq_exit();
 	set_irq_regs(old_regs);
 }
-
-void doorbell_check_self(void)
-{
-	struct doorbell_cpu_info *info = &__get_cpu_var(doorbell_cpu_info);
-
-	if (!info->messages)
-		return;
-
-	ppc_msgsnd(PPC_DBELL, 0, info->tag);
-}
-
 #else /* CONFIG_SMP */
 void doorbell_exception(struct pt_regs *regs)
 {
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index a81dd74414bf..826552cecebd 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -66,7 +66,6 @@
 #include <asm/ptrace.h>
 #include <asm/machdep.h>
 #include <asm/udbg.h>
-#include <asm/dbell.h>
 #include <asm/smp.h>
 
 #ifdef CONFIG_PPC64
@@ -160,7 +159,8 @@ notrace void arch_local_irq_restore(unsigned long en)
 
 #if defined(CONFIG_BOOKE) && defined(CONFIG_SMP)
 	/* Check for pending doorbell interrupts and resend to ourself */
-	doorbell_check_self();
+	if (cpu_has_feature(CPU_FTR_DBELL))
+		smp_muxed_ipi_resend();
 #endif
 
 	/*
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index b74411446922..fa8e8700064b 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -111,35 +111,6 @@ int __devinit smp_generic_kick_cpu(int nr)
 }
 #endif
 
-void smp_message_recv(int msg)
-{
-	switch(msg) {
-	case PPC_MSG_CALL_FUNCTION:
-		generic_smp_call_function_interrupt();
-		break;
-	case PPC_MSG_RESCHEDULE:
-		/* we notice need_resched on exit */
-		break;
-	case PPC_MSG_CALL_FUNC_SINGLE:
-		generic_smp_call_function_single_interrupt();
-		break;
-	case PPC_MSG_DEBUGGER_BREAK:
-		if (crash_ipi_function_ptr) {
-			crash_ipi_function_ptr(get_irq_regs());
-			break;
-		}
-#ifdef CONFIG_DEBUGGER
-		debugger_ipi(get_irq_regs());
-		break;
-#endif /* CONFIG_DEBUGGER */
-		/* FALLTHROUGH */
-	default:
-		printk("SMP %d: smp_message_recv(): unknown msg %d\n",
-		       smp_processor_id(), msg);
-		break;
-	}
-}
-
 static irqreturn_t call_function_action(int irq, void *data)
 {
 	generic_smp_call_function_interrupt();
@@ -158,9 +129,17 @@ static irqreturn_t call_function_single_action(int irq, void *data)
 	return IRQ_HANDLED;
 }
 
-static irqreturn_t debug_ipi_action(int irq, void *data)
+irqreturn_t debug_ipi_action(int irq, void *data)
 {
-	smp_message_recv(PPC_MSG_DEBUGGER_BREAK);
+	if (crash_ipi_function_ptr) {
+		crash_ipi_function_ptr(get_irq_regs());
+		return IRQ_HANDLED;
+	}
+
+#ifdef CONFIG_DEBUGGER
+	debugger_ipi(get_irq_regs());
+#endif /* CONFIG_DEBUGGER */
+
 	return IRQ_HANDLED;
 }
 
@@ -199,6 +178,59 @@ int smp_request_message_ipi(int virq, int msg)
 	return err;
 }
 
+struct cpu_messages {
+	unsigned long messages;		/* current messages bits */
+	unsigned long data;		/* data for cause ipi */
+};
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct cpu_messages, ipi_message);
+
+void smp_muxed_ipi_set_data(int cpu, unsigned long data)
+{
+	struct cpu_messages *info = &per_cpu(ipi_message, cpu);
+
+	info->data = data;
+}
+
+void smp_muxed_ipi_message_pass(int cpu, int msg)
+{
+	struct cpu_messages *info = &per_cpu(ipi_message, cpu);
+	unsigned long *tgt = &info->messages;
+
+	set_bit(msg, tgt);
+	mb();
+	smp_ops->cause_ipi(cpu, info->data);
+}
+
+void smp_muxed_ipi_resend(void)
+{
+	struct cpu_messages *info = &__get_cpu_var(ipi_message);
+	unsigned long *tgt = &info->messages;
+
+	if (*tgt)
+		smp_ops->cause_ipi(smp_processor_id(), info->data);
+}
+
+irqreturn_t smp_ipi_demux(void)
+{
+	struct cpu_messages *info = &__get_cpu_var(ipi_message);
+	unsigned long *tgt = &info->messages;
+
+	mb();	/* order any irq clear */
+	while (*tgt) {
+		if (test_and_clear_bit(PPC_MSG_CALL_FUNCTION, tgt))
+			generic_smp_call_function_interrupt();
+		if (test_and_clear_bit(PPC_MSG_RESCHEDULE, tgt))
+			reschedule_action(0, NULL); /* upcoming sched hook */
+		if (test_and_clear_bit(PPC_MSG_CALL_FUNC_SINGLE, tgt))
+			generic_smp_call_function_single_interrupt();
+#if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)
+		if (test_and_clear_bit(PPC_MSG_DEBUGGER_BREAK, tgt))
+			debug_ipi_action(0, NULL);
+#endif
+	}
+	return IRQ_HANDLED;
+}
+
 void smp_send_reschedule(int cpu)
 {
 	if (likely(smp_ops))