can: m_can: add device tree binding documentation

add M_CAN device tree binding documentation

Cc: Wolfgang Grandegger <wg@grandegger.com>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Dong Aisheng <b29396@freescale.com>
Reviewed-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Documentation/devicetree/bindings/net/can/m_can.txt

+Bosch MCAN controller Device Tree Bindings
+-------------------------------------------------
+
+Required properties:
+- compatible		: Should be "bosch,m_can" for M_CAN controllers
+- reg			: physical base address and size of the M_CAN
+			  registers map and Message RAM
+- reg-names		: Should be "m_can" and "message_ram"
+- interrupts		: Should be the interrupt number of M_CAN interrupt
+			  line 0 and line 1, could be same if sharing
+			  the same interrupt.
+- interrupt-names	: Should contain "int0" and "int1"
+- clocks		: Clocks used by controller, should be host clock
+			  and CAN clock.
+- clock-names		: Should contain "hclk" and "cclk"
+- pinctrl-<n>		: Pinctrl states as described in bindings/pinctrl/pinctrl-bindings.txt
+- pinctrl-names 	: Names corresponding to the numbered pinctrl states
+- bosch,mram-cfg	: Message RAM configuration data.
+			  Multiple M_CAN instances can share the same Message
+			  RAM and each element(e.g Rx FIFO or Tx Buffer and etc)
+			  number in Message RAM is also configurable,
+			  so this property is telling driver how the shared or
+			  private Message RAM are used by this M_CAN controller.
+
+			  The format should be as follows:
+			  <offset sidf_elems xidf_elems rxf0_elems rxf1_elems
+			   rxb_elems txe_elems txb_elems>
+			  The 'offset' is an address offset of the Message RAM
+			  where the following elements start from. This is
+			  usually set to 0x0 if you're using a private Message
+			  RAM. The remain cells are used to specify how many
+			  elements are used for each FIFO/Buffer.
+
+			  M_CAN includes the following elements according to user manual:
+			  11-bit Filter	0-128 elements / 0-128 words
+			  29-bit Filter	0-64 elements / 0-128 words
+			  Rx FIFO 0	0-64 elements / 0-1152 words
+			  Rx FIFO 1	0-64 elements / 0-1152 words
+			  Rx Buffers	0-64 elements / 0-1152 words
+			  Tx Event FIFO	0-32 elements / 0-64 words
+			  Tx Buffers	0-32 elements / 0-576 words
+
+			  Please refer to 2.4.1 Message RAM Configuration in
+			  Bosch M_CAN user manual for details.
+
+Example:
+SoC dtsi:
+m_can1: can@020e8000 {
+	compatible = "bosch,m_can";
+	reg = <0x020e8000 0x4000>, <0x02298000 0x4000>;
+	reg-names = "m_can", "message_ram";
+	interrupts = <0 114 0x04>,
+		     <0 114 0x04>;
+	interrupt-names = "int0", "int1";
+	clocks = <&clks IMX6SX_CLK_CANFD>,
+		 <&clks IMX6SX_CLK_CANFD>;
+	clock-names = "hclk", "cclk";
+	bosch,mram-cfg = <0x0 0 0 32 0 0 0 1>;
+	status = "disabled";
+};
+
+Board dts:
+&m_can1 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_m_can1>;
+	status = "enabled";
+};