metag: perf: fixes for interrupting perf counters

The overflow handler needs to read modify write when re-enabling the
counter so as not to change the counter value as it may have been
changed to ready the next interrupt on overflow. Similarly for
interrupting counters metag_pmu_enable_counter needs to leave the
counter value unchanged rather than resetting it to zero.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>

1 files changed, 15 insertions, 7 deletions

diff --git a/arch/metag/kernel/perf/perf_event.c b/arch/metag/kernel/perf/perf_event.c
index 8096db2a550b..a00f527eade5 100644
--- a/arch/metag/kernel/perf/perf_event.c
+++ b/arch/metag/kernel/perf/perf_event.c
@@ -643,13 +643,15 @@ static void metag_pmu_enable_counter(struct hw_perf_event *event, int idx)
                 config = tmp >> 4;
         }
 
-        /*
-         * Enabled counters start from 0. Early cores clear the count on
-         * write but newer cores don't, so we make sure that the count is
-         * set to 0.
-         */
         tmp = ((config & 0xf) << 28) |
                         ((1 << 24) << cpu_2_hwthread_id[get_cpu()]);
+        if (metag_pmu->max_period)
+                /*
+                 * Cores supporting overflow interrupts may have had the counter
+                 * set to a specific value that needs preserving.
+                 */
+                tmp |= metag_in32(PERF_COUNT(idx)) & 0x00ffffff;
+
         metag_out32(tmp, PERF_COUNT(idx));
 unlock:
         raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
@@ -764,10 +766,16 @@ static irqreturn_t metag_pmu_counter_overflow(int irq, void *dev)
 
         /*
          * Enable the counter again once core overflow processing has
-         * completed.
+         * completed. Note the counter value may have been modified while it was
+         * inactive to set it up ready for the next interrupt.
          */
-        if (!perf_event_overflow(event, &sampledata, regs))
+        if (!perf_event_overflow(event, &sampledata, regs)) {
+                __global_lock2(flags);
+                counter = (counter & 0xff000000) |
+                          (metag_in32(PERF_COUNT(idx)) & 0x00ffffff);
                 metag_out32(counter, PERF_COUNT(idx));
+                __global_unlock2(flags);
+        }
 
         return IRQ_HANDLED;
 }