[PATCH v3 1/2] dt-bindings: i2c: snps,designware-i2c: declare bus capacitance and clk freq optimized

[Michael Wu <michael.wu@kneron.us>]

Since there are no registers controlling the hardware parameters
IC_CAP_LOADING and IC_CLK_FREQ_OPTIMIZATION, their values can only be
declared in the device tree.

snps,bus-capacitance-pf indicates the bus capacitance in picofarads (pF).
It affects the high and low pulse width of SCL line in high speed mode.
The legal values for this property are 100 and 400 only, and default
value is 100. This property corresponds to IC_CAP_LOADING.

snps,clk-freq-optimized indicates whether the hardware input clock
frequency is reduced by reducing the internal latency. This property
corresponds to IC_CLK_FREQ_OPTIMIZATION.

The driver can calculate hs_hcnt and hs_lcnt appropriate for the hardware
based on these two properties.

Signed-off-by: Michael Wu <michael.wu@kneron.us>
---
 .../bindings/i2c/snps,designware-i2c.yaml     | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml b/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml
index 60035a787e5c..c373f3acd34b 100644
--- a/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml
+++ b/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml
@@ -97,6 +97,21 @@ properties:
       - const: tx
       - const: rx
 
+  snps,bus-capacitance-pf:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: >
+      This property indicates the bus capacitance in picofarads (pF).
+      This value is used to compute the tHIGH and tLOW periods for high speed
+      mode.
+    default: 100
+
+  snps,clk-freq-optimized:
+    description: >
+      This property indicates whether the hardware input clock frequency is
+      reduced by reducing the internal latency. This value is used to compute
+      the tHIGH and tLOW periods for high speed mode.
+    type: boolean
+
 unevaluatedProperties: false
 
 required:
@@ -146,4 +161,13 @@ examples:
       interrupts = <8>;
       clocks = <&ahb_clk>;
     };
+  - |
+    i2c@c5000000 {
+      compatible = "snps,designware-i2c";
+      reg = <0xc5000000 0x1000>;
+      interrupts = <37 1>;
+      clock-frequency = <400000>;
+      snps,bus-capacitance-pf = <400>;
+      snps,clk-freq-optimized;
+    };
 ...
-- 
2.43.0