intel_th: msu: Make stopping the trace optional

Some use cases prefer to keep collecting the trace data into the last
available window while the other windows are being offloaded instead of
stopping the trace. In this scenario, the window switch happens
automatically when the next window becomes available again.

Add an option to allow this and a sysfs attribute to enable it.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200319085152.52183-1-alexander.shishkin@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-bus-intel_th-devices-msc

@@ -40,3 +40,11 @@ Description:	(RW) Trigger window switch for the MSC's buffer, in
 		triggering a window switch for the buffer. Returns an error in any
 		other operating mode or attempts to write something other than "1".
 
+What:		/sys/bus/intel_th/devices/<intel_th_id>-msc<msc-id>/stop_on_full
+Date:		March 2020
+KernelVersion:	5.7
+Contact:	Alexander Shishkin <alexander.shishkin@linux.intel.com>
+Description:	(RW) Configure whether trace stops when the last available window
+		becomes full (1/y/Y) or wraps around and continues until the next
+		window becomes available again (0/n/N).
+

drivers/hwtracing/intel_th/msu.c

@@ -138,6 +138,7 @@ struct msc {
 	struct list_head	win_list;
 	struct sg_table		single_sgt;
 	struct msc_window	*cur_win;
+	struct msc_window	*switch_on_unlock;
 	unsigned long		nr_pages;
 	unsigned long		single_sz;
 	unsigned int		single_wrap : 1;
@@ -154,6 +155,8 @@ struct msc {
 
 	struct list_head	iter_list;
 
+	bool			stop_on_full;
+
 	/* config */
 	unsigned int		enabled : 1,
 				wrap	: 1,
@@ -1718,6 +1721,10 @@ void intel_th_msc_window_unlock(struct device *dev, struct sg_table *sgt)
 		return;
 
 	msc_win_set_lockout(win, WIN_LOCKED, WIN_READY);
+	if (msc->switch_on_unlock == win) {
+		msc->switch_on_unlock = NULL;
+		msc_win_switch(msc);
+	}
 }
 EXPORT_SYMBOL_GPL(intel_th_msc_window_unlock);
 
@@ -1758,7 +1765,11 @@ static irqreturn_t intel_th_msc_interrupt(struct intel_th_device *thdev)
 
 	/* next window: if READY, proceed, if LOCKED, stop the trace */
 	if (msc_win_set_lockout(next_win, WIN_READY, WIN_INUSE)) {
+		if (msc->stop_on_full)
 			schedule_work(&msc->work);
+		else
+			msc->switch_on_unlock = next_win;
+
 		return IRQ_HANDLED;
 	}
 
@@ -2051,11 +2062,36 @@ win_switch_store(struct device *dev, struct device_attribute *attr,
 
 static DEVICE_ATTR_WO(win_switch);
 
+static ssize_t stop_on_full_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct msc *msc = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%d\n", msc->stop_on_full);
+}
+
+static ssize_t stop_on_full_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t size)
+{
+	struct msc *msc = dev_get_drvdata(dev);
+	int ret;
+
+	ret = kstrtobool(buf, &msc->stop_on_full);
+	if (ret)
+		return ret;
+
+	return size;
+}
+
+static DEVICE_ATTR_RW(stop_on_full);
+
 static struct attribute *msc_output_attrs[] = {
 	&dev_attr_wrap.attr,
 	&dev_attr_mode.attr,
 	&dev_attr_nr_pages.attr,
 	&dev_attr_win_switch.attr,
+	&dev_attr_stop_on_full.attr,
 	NULL,
 };