1 files changed, 16 insertions, 2 deletions

diff --git a/Documentation/devicetree/bindings/i2c/i2c-ocores.txt b/Documentation/devicetree/bindings/i2c/i2c-ocores.txt
index 1637c298a1b3..5bef3adf2c35 100644
--- a/Documentation/devicetree/bindings/i2c/i2c-ocores.txt
+++ b/Documentation/devicetree/bindings/i2c/i2c-ocores.txt
@@ -4,15 +4,29 @@ Required properties:
 - compatible      : "opencores,i2c-ocores" or "aeroflexgaisler,i2cmst"
 - reg             : bus address start and address range size of device
 - interrupts      : interrupt number
-- clock-frequency : frequency of bus clock in Hz
+- opencores,ip-clock-frequency: frequency of the controller clock in Hz;
+                    see the note below
 - #address-cells  : should be <1>
 - #size-cells     : should be <0>
 
 Optional properties:
+- clock-frequency : frequency of bus clock in Hz; see the note below.
+                    Defaults to 100 KHz when the property is not specified
 - reg-shift       : device register offsets are shifted by this value
 - reg-io-width    : io register width in bytes (1, 2 or 4)
 - regstep         : deprecated, use reg-shift above
 
+Note
+clock-frequency property is meant to control the bus frequency for i2c bus
+drivers, but it was incorrectly used to specify i2c controller input clock
+frequency. So the following rules are set to fix this situation:
+- if clock-frequency is present and opencores,ip-clock-frequency is not,
+  then clock-frequency specifies i2c controller clock frequency. This is
+  to keep backwards compatibility with setups using old DTB. i2c bus
+  frequency is fixed at 100 KHz.
+- if opencores,ip-clock-frequency is present it specifies i2c controller
+  clock frequency. clock-frequency property specifies i2c bus frequency.
+
 Example:
 
         i2c0: ocores@a0000000 {
@@ -21,7 +35,7 @@ Example:
                 compatible = "opencores,i2c-ocores";
                 reg = <0xa0000000 0x8>;
                 interrupts = <10>;
-                clock-frequency = <20000000>;
+                opencores,ip-clock-frequency = <20000000>;
 
                 reg-shift = <0>;        /* 8 bit registers */
                 reg-io-width = <1>;     /* 8 bit read/write */