stm class: Add a helper for writing data packets

Add a helper to write a sequence of bytes as STP data packets. This
is used by protocol drivers to output their metadata, as well as the
actual data payload.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 41 insertions, 13 deletions

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index 915af2541dcd..b789a5f0688e 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -569,27 +569,52 @@ stm_assign_first_policy(struct stm_device *stm, struct stm_output *output,
         return err;
 }
 
-static ssize_t notrace stm_write(struct stm_data *data, unsigned int master,
-                          unsigned int channel, const char *buf, size_t count)
+/**
+ * stm_data_write() - send the given payload as data packets
+ * @data:       stm driver's data
+ * @m:          STP master
+ * @c:          STP channel
+ * @ts_first:   timestamp the first packet
+ * @buf:        data payload buffer
+ * @count:      data payload size
+ */
+ssize_t notrace stm_data_write(struct stm_data *data, unsigned int m,
+                               unsigned int c, bool ts_first, const void *buf,
+                               size_t count)
 {
-        unsigned int flags = STP_PACKET_TIMESTAMPED;
-        const unsigned char *p = buf, nil = 0;
-        size_t pos;
+        unsigned int flags = ts_first ? STP_PACKET_TIMESTAMPED : 0;
         ssize_t sz;
+        size_t pos;
 
-        for (pos = 0, p = buf; count > pos; pos += sz, p += sz) {
+        for (pos = 0, sz = 0; pos < count; pos += sz) {
                 sz = min_t(unsigned int, count - pos, 8);
-                sz = data->packet(data, master, channel, STP_PACKET_DATA, flags,
-                                  sz, p);
-                flags = 0;
-
-                if (sz < 0)
+                sz = data->packet(data, m, c, STP_PACKET_DATA, flags, sz,
+                                  &((u8 *)buf)[pos]);
+                if (sz <= 0)
                         break;
+
+                if (ts_first) {
+                        flags = 0;
+                        ts_first = false;
+                }
         }
 
-        data->packet(data, master, channel, STP_PACKET_FLAG, 0, 0, &nil);
+        return sz < 0 ? sz : pos;
+}
+EXPORT_SYMBOL_GPL(stm_data_write);
+
+static ssize_t notrace stm_write(struct stm_data *data, unsigned int master,
+                          unsigned int channel, const char *buf, size_t count)
+{
+        const unsigned char nil = 0;
+        ssize_t sz;
+
+        sz = stm_data_write(data, master, channel, true, buf, count);
+        if (sz > 0)
+                data->packet(data, master, channel, STP_PACKET_FLAG, 0, 0,
+                             &nil);
 
-        return pos;
+        return sz;
 }
 
 static ssize_t stm_char_write(struct file *file, const char __user *buf,
diff --git a/drivers/hwtracing/stm/stm.h b/drivers/hwtracing/stm/stm.h
index ed7f3d07fa47..3569439d53bb 100644
--- a/drivers/hwtracing/stm/stm.h
+++ b/drivers/hwtracing/stm/stm.h
@@ -110,5 +110,8 @@ int stm_lookup_protocol(const char *name,
                         const struct stm_protocol_driver **pdrv,
                         const struct config_item_type **type);
 void stm_put_protocol(const struct stm_protocol_driver *pdrv);
+ssize_t stm_data_write(struct stm_data *data, unsigned int m,
+                       unsigned int c, bool ts_first, const void *buf,
+                       size_t count);
 
 #endif /* _STM_STM_H_ */