[PATCH] drivers: power: reset: at91-reset: Provide reset reason via sysfs.

[David Mosberger-Tang]

Rather than just printing the reset-reason at boot-time, make it available
via sysfs as attribute "reset_reason" of the reset controller.  For example,
on SAMA5D2 Xplained, this sysfs attribute is available at:

 /sys/devices/platform/ahb/ahb:apb/f8048000.rstc/reset_reason
---
 drivers/power/reset/at91-reset.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/drivers/power/reset/at91-reset.c b/drivers/power/reset/at91-reset.c
index 264b9b8..184516b 100644
--- a/drivers/power/reset/at91-reset.c
+++ b/drivers/power/reset/at91-reset.c
@@ -45,6 +45,11 @@ enum reset_type {
 	RESET_TYPE_USER		= 4,
 };
 
+static ssize_t reset_reason_show(struct device *,
+				 struct device_attribute *attr,
+				 char *);
+static DEVICE_ATTR(reset_reason, S_IRUSR, reset_reason_show, NULL);
+
 static void __iomem *at91_ramc_base[2], *at91_rstc_base;
 
 /*
@@ -132,7 +137,7 @@ static int sama5d3_restart(struct notifier_block *this, unsigned long mode,
 	return NOTIFY_DONE;
 }
 
-static void __init at91_reset_status(struct platform_device *pdev)
+static const char *at91_reset_reason(struct platform_device *pdev)
 {
 	u32 reg = readl(at91_rstc_base + AT91_RSTC_SR);
 	char *reason;
@@ -157,8 +162,15 @@ static void __init at91_reset_status(struct platform_device *pdev)
 		reason = "unknown reset";
 		break;
 	}
+	return reason;
+}
 
-	pr_info("AT91: Starting after %s\n", reason);
+static ssize_t reset_reason_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	return strcpy(buf, at91_reset_reason(pdev));
 }
 
 static const struct of_device_id at91_ramc_of_match[] = {
@@ -250,7 +262,13 @@ static int at91_reset_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	at91_reset_status(pdev);
+	ret = device_create_file(&pdev->dev, &dev_attr_reset_reason);
+	if (ret) {
+		dev_err(&pdev->dev, "Could not create sysfs entry\n");
+		return ret;
+	}
+
+	pr_info("AT91: Starting after %s\n", at91_reset_reason(pdev));
 
 	return 0;
 }
-- 
1.9.1