2 files changed, 33 insertions, 4 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index e2a4ff6fc3a6..58a93fbd68aa 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -302,4 +302,27 @@ config FTRACE_STARTUP_TEST
           functioning properly. It will do tests on all the configured
           tracers of ftrace.
 
+config MMIOTRACE
+        bool "Memory mapped IO tracing"
+        depends on HAVE_MMIOTRACE_SUPPORT && DEBUG_KERNEL && PCI
+        select TRACING
+        help
+          Mmiotrace traces Memory Mapped I/O access and is meant for
+          debugging and reverse engineering. It is called from the ioremap
+          implementation and works via page faults. Tracing is disabled by
+          default and can be enabled at run-time.
+
+          See Documentation/tracers/mmiotrace.txt.
+          If you are not helping to develop drivers, say N.
+
+config MMIOTRACE_TEST
+        tristate "Test module for mmiotrace"
+        depends on MMIOTRACE && m
+        help
+          This is a dumb module for testing mmiotrace. It is very dangerous
+          as it will write garbage to IO memory starting at a given address.
+          However, it should be safe to use on e.g. unused portion of VRAM.
+
+          Say N, unless you absolutely know what you are doing.
+
 endmenu
diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
index fffcb069f1dc..80e503ef6136 100644
--- a/kernel/trace/trace_mmiotrace.c
+++ b/kernel/trace/trace_mmiotrace.c
@@ -9,6 +9,7 @@
 #include <linux/kernel.h>
 #include <linux/mmiotrace.h>
 #include <linux/pci.h>
+#include <asm/atomic.h>
 
 #include "trace.h"
 
@@ -19,6 +20,7 @@ struct header_iter {
 static struct trace_array *mmio_trace_array;
 static bool overrun_detected;
 static unsigned long prev_overruns;
+static atomic_t dropped_count;
 
 static void mmio_reset_data(struct trace_array *tr)
 {
@@ -121,11 +123,11 @@ static void mmio_close(struct trace_iterator *iter)
 
 static unsigned long count_overruns(struct trace_iterator *iter)
 {
-        unsigned long cnt = 0;
+        unsigned long cnt = atomic_xchg(&dropped_count, 0);
         unsigned long over = ring_buffer_overruns(iter->tr->buffer);
 
         if (over > prev_overruns)
-                cnt = over - prev_overruns;
+                cnt += over - prev_overruns;
         prev_overruns = over;
         return cnt;
 }
@@ -310,8 +312,10 @@ static void __trace_mmiotrace_rw(struct trace_array *tr,
 
         event   = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry),
                                            &irq_flags);
-        if (!event)
+        if (!event) {
+                atomic_inc(&dropped_count);
                 return;
+        }
         entry   = ring_buffer_event_data(event);
         tracing_generic_entry_update(&entry->ent, 0, preempt_count());
         entry->ent.type                 = TRACE_MMIO_RW;
@@ -338,8 +342,10 @@ static void __trace_mmiotrace_map(struct trace_array *tr,
 
         event   = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry),
                                            &irq_flags);
-        if (!event)
+        if (!event) {
+                atomic_inc(&dropped_count);
                 return;
+        }
         entry   = ring_buffer_event_data(event);
         tracing_generic_entry_update(&entry->ent, 0, preempt_count());
         entry->ent.type                 = TRACE_MMIO_MAP;