linux-kernel - [PATCH 2/2] clocksource: Add suspend clocksource sysfs attribute

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Date:   Fri, 14 Jun 2019 12:45:10 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] clocksource: Add suspend clocksource sysfs attribute

From: Thierry Reding <treding@...dia.com>

Allow the currently selected suspend clocksource to be inspected via
sysfs. The suspend clocksource can also be set using this attribute,
which can be useful for debugging.

Signed-off-by: Thierry Reding <treding@...dia.com>
---
 kernel/time/clocksource.c | 53 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 52 insertions(+), 1 deletion(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 467b36d2f9f8..d963bcecbc96 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -489,7 +489,8 @@ static void __clocksource_suspend_select(struct clocksource *cs)
 	}
 
 	/* Pick the best rating. */
-	if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
+	if (!suspend_clocksource || cs->rating > suspend_clocksource->rating ||
+	    (suspend_clocksource->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) == 0)
 		suspend_clocksource = cs;
 }
 
@@ -1172,10 +1173,60 @@ static ssize_t available_clocksource_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(available_clocksource);
 
+static ssize_t suspend_clocksource_show(struct device *dev,
+					struct device_attribute *attr,
+					char *buf)
+{
+	struct clocksource *clksrc = suspend_clocksource;
+	ssize_t count = 0;
+
+	if (clksrc)
+		count += snprintf(buf, PAGE_SIZE, "%s\n", clksrc->name);
+
+	return count;
+}
+
+static ssize_t suspend_clocksource_store(struct device *dev,
+					 struct device_attribute *attr,
+					 const char *buf, size_t count)
+{
+	struct clocksource *cs;
+	char name[CS_NAME_LEN];
+	ssize_t ret;
+
+	ret = sysfs_get_uname(buf, name, count);
+	if (ret < 0)
+		return ret;
+
+	mutex_lock(&clocksource_mutex);
+
+	if (strlen(name) > 0) {
+		cs = clocksource_lookup(name);
+		if (cs) {
+			if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
+				pr_warn("using non-persistent clocksource %s for suspend\n",
+					cs->name);
+
+			suspend_clocksource = cs;
+		} else {
+			ret = -ENODEV;
+		}
+	} else {
+		clocksource_suspend_select(false);
+	}
+
+	mutex_unlock(&clocksource_mutex);
+
+	return ret ? ret : count;
+}
+
+static DEVICE_ATTR_RW(suspend_clocksource);
+
 static struct attribute *clocksource_attrs[] = {
 	&dev_attr_current_clocksource.attr,
 	&dev_attr_unbind_clocksource.attr,
 	&dev_attr_available_clocksource.attr,
+	&dev_attr_suspend_clocksource.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(clocksource);
-- 
2.21.0