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authorUwe Kleine-König <u.kleine-koenig@pengutronix.de>2015-04-16 12:45:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-04-17 09:03:59 -0400
commit7f48b21bdfede2c06e966258317a3bb4be3e4f25 (patch)
tree97bbc064215190a72387d0607afadc92cc39c76c /Documentation/devicetree/bindings/rtc
parentb0c57b5941c4a42698d845ada6a76feeba2d1be9 (diff)
rtc: stmp3xxx: use optional crystal in low power states
The rtc's status register allows to determine if a 32k crystal is connected to keep the rtc running in low power states provided the corresponding fuse bits were blown correctly during production. (In case they were not, the right frequency can be stated in the device tree.) If there is no such crystal available force the 24 MHz XTAL clock to keep running to retain the right date and time. Otherwise use the crystal to save some power. It would be nice to only switch to the crystal when the XTAL clock is about to be disabled and keep the crystal off when unneeded because XTAL is always on while the chip is powered on. But as sudden power loss isn't detectable this is not save. Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Cc: Alessandro Zummo <a.zummo@towertech.it> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/devicetree/bindings/rtc')
-rw-r--r--Documentation/devicetree/bindings/rtc/stmp3xxx-rtc.txt5
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/rtc/stmp3xxx-rtc.txt b/Documentation/devicetree/bindings/rtc/stmp3xxx-rtc.txt
index b800070fe6e9..fa6a94226669 100644
--- a/Documentation/devicetree/bindings/rtc/stmp3xxx-rtc.txt
+++ b/Documentation/devicetree/bindings/rtc/stmp3xxx-rtc.txt
@@ -7,6 +7,11 @@ Required properties:
region.
- interrupts: rtc alarm interrupt
+Optional properties:
+- stmp,crystal-freq: override crystal frequency as determined from fuse bits.
+ Only <32000> and <32768> are possible for the hardware. Use <0> for
+ "no crystal".
+
Example:
rtc@80056000 {