stm class: Switch over to the protocol driver

Now that the default framing protocol is factored out into its own driver,
switch over to using the driver for writing data. To that end, make the
policy code require a valid protocol name (or absence thereof, which is
equivalent to "p_basic").

Also, to make transition easier, make stm class request "p_basic" module
at initialization time.
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>

drivers/hwtracing/stm/core.c

@@ -603,18 +603,21 @@ ssize_t notrace stm_data_write(struct stm_data *data, unsigned int m,
 }
 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)
+static ssize_t notrace
+stm_write(struct stm_device *stm, struct stm_output *output,
+	  unsigned int chan, const char *buf, size_t count)
 {
-	const unsigned char nil = 0;
-	ssize_t sz;
+	int err;
+
+	/* stm->pdrv is serialized against policy_mutex */
+	if (!stm->pdrv)
+		return -ENODEV;
 
-	sz = stm_data_write(data, master, channel, true, buf, count);
-	if (sz > 0)
-		data->packet(data, master, channel, STP_PACKET_FLAG, 0, 0,
-			     &nil);
+	err = stm->pdrv->write(stm->data, output, chan, buf, count);
+	if (err < 0)
+		return err;
 
-	return sz;
+	return err;
 }
 
 static ssize_t stm_char_write(struct file *file, const char __user *buf,
@@ -659,8 +662,7 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
 
 	pm_runtime_get_sync(&stm->dev);
 
-	count = stm_write(stm->data, stmf->output.master, stmf->output.channel,
-			  kbuf, count);
+	count = stm_write(stm, &stmf->output, 0, kbuf, count);
 
 	pm_runtime_mark_last_busy(&stm->dev);
 	pm_runtime_put_autosuspend(&stm->dev);
@@ -1310,9 +1312,7 @@ int notrace stm_source_write(struct stm_source_data *data,
 
 	stm = srcu_dereference(src->link, &stm_source_srcu);
 	if (stm)
-		count = stm_write(stm->data, src->output.master,
-				  src->output.channel + chan,
-				  buf, count);
+		count = stm_write(stm, &src->output, chan, buf, count);
 	else
 		count = -ENODEV;
 
@@ -1342,6 +1342,12 @@ static int __init stm_core_init(void)
 	INIT_LIST_HEAD(&stm_pdrv_head);
 	mutex_init(&stm_pdrv_mutex);
 
+	/*
+	 * So as to not confuse existing users with a requirement
+	 * to load yet another module, do it here.
+	 */
+	if (IS_ENABLED(CONFIG_STM_PROTO_BASIC))
+		(void)request_module_nowait("stm_p_basic");
 	stm_core_up++;
 
 	return 0;

drivers/hwtracing/stm/policy.c

@@ -454,8 +454,7 @@ stp_policy_make(struct config_group *group, const char *name)
 	err = stm_lookup_protocol(proto, &pdrv, &pdrv_node_type);
 	kfree(devname);
 
-	/* We don't have any protocol drivers yet */
-	if (err != -ENOENT) {
+	if (err) {
 		stm_put_device(stm);
 		return ERR_PTR(-ENODEV);
 	}