[PATCH] i2c: add 'single-master' property to generic bindings

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

It is useful to know if we are the only master on a given bus. Because
this is a HW description of the bus, add it to the generic bindings.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Laine Jaakko EXT <ext-jaakko.laine@vaisala.com>
---

We added 'multi-master' back then because most busses are single-master
and 'multi-master' was the exception. In hindsight, however, this was a
bad choice because 'multi-master' should be the default, i.e. if you
know nothing, you should assume there could be another master.

So, we can't deduce that a missing 'multi-master' property automatically
means 'single-master'. That's why we need this new property.

I am a bit tempted to mark 'multi-master' as deprecated because the
default should be multi-master. However, it might also be a bit more
descriptive to let "no property" still mean "we don't know". I'd be
thankful for more opinions here.

Thanks and happy hacking,

   Wolfram

 Documentation/devicetree/bindings/i2c/i2c.txt | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
index 819436b48fae..438ae123107e 100644
--- a/Documentation/devicetree/bindings/i2c/i2c.txt
+++ b/Documentation/devicetree/bindings/i2c/i2c.txt
@@ -70,7 +70,12 @@ wants to support one of the below features, it should adapt these bindings.
 - multi-master
 	states that there is another master active on this bus. The OS can use
 	this information to adapt power management to keep the arbitration awake
-	all the time, for example.
+	all the time, for example. Can not be combined with 'single-master'.
+
+- single-master
+	states that there is no other master active on this bus. The OS can use
+	this information to detect a stalled bus more reliably, for example.
+	Can not be combined with 'multi-master'.
 
 Required properties (per child device)
 --------------------------------------
-- 
2.20.1