1 files changed, 70 insertions, 54 deletions

diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
index c2f9ebbc38f6..40859e5619f9 100644
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -197,51 +197,65 @@ int __init setup_profiling_timer(unsigned int multiplier)
 /*              Inter Processor Interrupt Handling                           */
 /*****************************************************************************/
 
-/*
- * structures for inter-processor calls
- * A Collection of single bit ipi messages
- *
- */
-
-/*
- * TODO_rajesh investigate tlb message types.
- * IPI Timer not needed because each ARC has an individual Interrupting Timer
- */
 enum ipi_msg_type {
-        IPI_NOP = 0,
+        IPI_EMPTY = 0,
         IPI_RESCHEDULE = 1,
         IPI_CALL_FUNC,
-        IPI_CPU_STOP
+        IPI_CPU_STOP,
 };
 
-struct ipi_data {
-        unsigned long bits;
-};
+/*
+ * In arches with IRQ for each msg type (above), receiver can use IRQ-id  to
+ * figure out what msg was sent. For those which don't (ARC has dedicated IPI
+ * IRQ), the msg-type needs to be conveyed via per-cpu data
+ */
 
-static DEFINE_PER_CPU(struct ipi_data, ipi_data);
+static DEFINE_PER_CPU(unsigned long, ipi_data);
 
-static void ipi_send_msg(const struct cpumask *callmap, enum ipi_msg_type msg)
+static void ipi_send_msg_one(int cpu, enum ipi_msg_type msg)
 {
+        unsigned long __percpu *ipi_data_ptr = per_cpu_ptr(&ipi_data, cpu);
+        unsigned long old, new;
         unsigned long flags;
-        unsigned int cpu;
+
+        pr_debug("%d Sending msg [%d] to %d\n", smp_processor_id(), msg, cpu);
 
         local_irq_save(flags);
 
-        for_each_cpu(cpu, callmap) {
-                struct ipi_data *ipi = &per_cpu(ipi_data, cpu);
-                set_bit(msg, &ipi->bits);
-        }
+        /*
+         * Atomically write new msg bit (in case others are writing too),
+         * and read back old value
+         */
+        do {
+                new = old = *ipi_data_ptr;
+                new |= 1U << msg;
+        } while (cmpxchg(ipi_data_ptr, old, new) != old);
 
-        /* Call the platform specific cross-CPU call function  */
-        if (plat_smp_ops.ipi_send)
-                plat_smp_ops.ipi_send((void *)callmap);
+        /*
+         * Call the platform specific IPI kick function, but avoid if possible:
+         * Only do so if there's no pending msg from other concurrent sender(s).
+         * Otherwise, recevier will see this msg as well when it takes the
+         * IPI corresponding to that msg. This is true, even if it is already in
+         * IPI handler, because !@old means it has not yet dequeued the msg(s)
+         * so @new msg can be a free-loader
+         */
+        if (plat_smp_ops.ipi_send && !old)
+                plat_smp_ops.ipi_send(cpu);
 
         local_irq_restore(flags);
 }
 
+static void ipi_send_msg(const struct cpumask *callmap, enum ipi_msg_type msg)
+{
+        unsigned int cpu;
+
+        for_each_cpu(cpu, callmap)
+                ipi_send_msg_one(cpu, msg);
+}
+
 void smp_send_reschedule(int cpu)
 {
-        ipi_send_msg(cpumask_of(cpu), IPI_RESCHEDULE);
+        ipi_send_msg_one(cpu, IPI_RESCHEDULE);
 }
 
 void smp_send_stop(void)
@@ -254,7 +268,7 @@ void smp_send_stop(void)
 
 void arch_send_call_function_single_ipi(int cpu)
 {
-        ipi_send_msg(cpumask_of(cpu), IPI_CALL_FUNC);
+        ipi_send_msg_one(cpu, IPI_CALL_FUNC);
 }
 
 void arch_send_call_function_ipi_mask(const struct cpumask *mask)
@@ -265,33 +279,29 @@ void arch_send_call_function_ipi_mask(const struct cpumask *mask)
 /*
  * ipi_cpu_stop - handle IPI from smp_send_stop()
  */
-static void ipi_cpu_stop(unsigned int cpu)
+static void ipi_cpu_stop(void)
 {
         machine_halt();
 }
 
-static inline void __do_IPI(unsigned long *ops, struct ipi_data *ipi, int cpu)
+static inline void __do_IPI(unsigned long msg)
 {
-        unsigned long msg = 0;
+        switch (msg) {
+        case IPI_RESCHEDULE:
+                scheduler_ipi();
+                break;
 
-        do {
-                msg = find_next_bit(ops, BITS_PER_LONG, msg+1);
+        case IPI_CALL_FUNC:
+                generic_smp_call_function_interrupt();
+                break;
 
-                switch (msg) {
-                case IPI_RESCHEDULE:
-                        scheduler_ipi();
-                        break;
-
-                case IPI_CALL_FUNC:
-                        generic_smp_call_function_interrupt();
-                        break;
-
-                case IPI_CPU_STOP:
-                        ipi_cpu_stop(cpu);
-                        break;
-                }
-        } while (msg < BITS_PER_LONG);
+        case IPI_CPU_STOP:
+                ipi_cpu_stop();
+                break;
 
+        default:
+                pr_warn("IPI with unexpected msg %ld\n", msg);
+        }
 }
 
 /*
@@ -300,19 +310,25 @@ static inline void __do_IPI(unsigned long *ops, struct ipi_data *ipi, int cpu)
  */
 irqreturn_t do_IPI(int irq, void *dev_id)
 {
-        int cpu = smp_processor_id();
-        struct ipi_data *ipi = &per_cpu(ipi_data, cpu);
-        unsigned long ops;
+        unsigned long pending;
+
+        pr_debug("IPI [%ld] received on cpu %d\n",
+                 *this_cpu_ptr(&ipi_data), smp_processor_id());
 
         if (plat_smp_ops.ipi_clear)
-                plat_smp_ops.ipi_clear(cpu, irq);
+                plat_smp_ops.ipi_clear(irq);
 
         /*
-         * XXX: is this loop really needed
-         * And do we need to move ipi_clean inside
+         * "dequeue" the msg corresponding to this IPI (and possibly other
+         * piggybacked msg from elided IPIs: see ipi_send_msg_one() above)
          */
-        while ((ops = xchg(&ipi->bits, 0)) != 0)
-                __do_IPI(&ops, ipi, cpu);
+        pending = xchg(this_cpu_ptr(&ipi_data), 0);
+
+        do {
+                unsigned long msg = __ffs(pending);
+                __do_IPI(msg);
+                pending &= ~(1U << msg);
+        } while (pending);
 
         return IRQ_HANDLED;
 }