The property clock-frequency is optional for device tree probe. When
it's absent, the flexcan driver will try to get the frequency from clk
system by calling clk_get_rate.
But, the clk_get_rate requires that clocks and clock-names properties
to be present in the flexcan node.
Document the usage of these properties.
Signed-off-by: Pankaj Bansal <pankaj.bansal@xxxxxxx>
---
Notes:
V2:
- Added notes that mentioning clocks' phandles is preferred method
over mentioning clock-frequency
.../bindings/net/can/fsl-flexcan.txt | 37 ++++++++++++++++--
1 file changed, 34 insertions(+), 3 deletions(-)
diff --git a/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt b/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
index bfc0c433654f..e1f9cc17d818 100644
--- a/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
+++ b/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
@@ -12,10 +12,29 @@ Required properties:
- reg : Offset and length of the register set for this device
- interrupts : Interrupt tuple for this device
-Optional properties:
+The input clock is the one fed to the prescaler to generate the serial clock
+(Sclock). Serial Clock (Sclock), whose period defines the 'time quantum'
+used to compose the CAN waveform. The input clock information can be given
+in two formats
+
+- clocks: phandle to the clocks feeding the SPI controller. Two can be given:
+ - "ipg": Oscillator Clock
+ - "per": Peripheral Clock
+- clock-names: Must contain the clock names described just above
+Note : This method is preferred method.
+
+ or
+
+- clock-frequency : The oscillator/peripheral clock frequency
+ driving the flexcan device.
+Note : Only on platforms where you don't have your clocks in the Device Tree,
+ use "clock-frequency" (as a fallback).
-- clock-frequency : The oscillator frequency driving the flexcan device
+The oscillator clock should be selected whenever a tight tolerance (up to 0.1%)
+is required in the CAN bus timing. The crystal oscillator clock has better
+jitter performance than the peripheral clock.
+Optional properties:
- xceiver-supply: Regulator that powers the CAN transceiver
- big-endian: This means the registers of FlexCAN controller are big endian.
@@ -25,11 +44,23 @@ Optional properties:
endian.
Example:
+ can0: can@2180000 {
+ compatible = "fsl,lx2160ar1-flexcan";
+ reg = <0x0 0x2180000 0x0 0x10000>;
+ interrupts = <GIC_SPI 21 IRQ_TYPE_LEVEL_HIGH>;
+ clocks = <&clockgen 4 7>, <&clockgen 4 7>; // preferred method
+ clock-names = "ipg", "per";
+ status = "disabled";
+ };
can@1c000 {
compatible = "fsl,p1010-flexcan";
reg = <0x1c000 0x1000>;
interrupts = <48 0x2>;
interrupt-parent = <&mpic>;
- clock-frequency = <200000000>; // filled in by bootloader
+ clock-frequency = <200000000>; // fallback method if no clocks
+ // in device tree. can be filled
+ // by bootloader
+ big-endian;
};
+
--
2.17.1
