On Thu, May 18, 2017 at 05:56:31PM +0200, Alexandre Belloni wrote:

Hi,

On 18/05/2017 at 16:45:21 +0200, Michael Thalmeier wrote:

quoted

To detect when the backup power domain has lost power a software defined bit
is set in one of the general purpose persistent registers when writing a new
time into the rtc.
When reading the time this bit is checked to determine if a power fail has
happened since the last time the rtc time was set.

I'm kind of concerned that other people may want to use those register
for something else but I don't currently have anything better to
suggest.

The other concern is that when updating the kernel, this will make amm
the rtc report that the time is invalid until the next update. So this
should be disabled by default.

How would you think this is best to disable by default? With a config
option or with a module parameter?
Either way would also allow to make the bit mask in the PERSISTENT2
register configurable, so one can use whichever bit is still unused by
some other applications.

quoted

When we detect a power fail we return -ENODATA.

All the other drivers return -EINVAL in that case.

quoted

Signed-off-by: Michael Thalmeier <redacted>
---
 drivers/rtc/rtc-stmp3xxx.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/rtc/rtc-stmp3xxx.c b/drivers/rtc/rtc-stmp3xxx.c
index d578e40..51330ec 100644
--- a/drivers/rtc/rtc-stmp3xxx.c
+++ b/drivers/rtc/rtc-stmp3xxx.c

@@ -62,6 +62,9 @@
 /* missing bitmask in headers */
 #define STMP3XXX_RTC_PERSISTENT1_FORCE_UPDATER	0x80000000
 
+#define STMP3XXX_RTC_PERSISTENT2		0x80
+#define STMP3XXX_RTC_PERSISTENT2_VALID_TIME	0x01
+
 struct stmp3xxx_rtc_data {
 	struct rtc_device *rtc;
 	void __iomem *io;

@@ -160,6 +163,10 @@ static int stmp3xxx_rtc_gettime(struct device *dev, struct rtc_time *rtc_tm)
 	if (ret)
 		return ret;
 
+	if (!(readl(rtc_data->io + STMP3XXX_RTC_PERSISTENT2) &
+				STMP3XXX_RTC_PERSISTENT2_VALID_TIME))
+		return -ENODATA;
+
 	rtc_time_to_tm(readl(rtc_data->io + STMP3XXX_RTC_SECONDS), rtc_tm);
 	return 0;
 }

@@ -169,6 +176,8 @@ static int stmp3xxx_rtc_set_mmss(struct device *dev, unsigned long t)
 	struct stmp3xxx_rtc_data *rtc_data = dev_get_drvdata(dev);
 
 	writel(t, rtc_data->io + STMP3XXX_RTC_SECONDS);
+	writel(STMP3XXX_RTC_PERSISTENT2_VALID_TIME,
+		rtc_data->io + STMP3XXX_RTC_PERSISTENT2 + STMP_OFFSET_REG_SET);
 	return stmp3xxx_wait_time(rtc_data);
 }
 

-- 
2.9.2

-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

-- 

Michael Thalmeier
(Entwicklung)
HALE electronic GmbH
Eugen-Müller-Straße 18, 5020 Salzburg, Austria
Tel: +43 (662) 439011 0
Fax: +43 (662) 439011 9
michael.thalmeier@hale.at
Firmenbuchnummer: FN 66801m HG Salzburg