[PATCH v6 4/4] DT: pdm: Add binding document for IMG PDM DAC

[Naidu Tellapati <naidu.tellapati@gmail.com>]

Add binding document for the Pulse Density Modulator (PDM) DAC present on the
Pistachio SOC.

Signed-off-by: Naidu Tellapati <Naidu.Tellapati@imgtec.com>
Signed-off-by: Arul Ramasamy <Arul.Ramasamy@imgtec.com>
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 Documentation/devicetree/bindings/misc/img-pdm.txt |   54 ++++++++++++++++++++
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 create mode 100644 Documentation/devicetree/bindings/misc/img-pdm.txt

diff --git a/Documentation/devicetree/bindings/misc/img-pdm.txt b/Documentation/devicetree/bindings/misc/img-pdm.txt
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+*Imagination Technologies Pulse Density Modulator (PDM) DAC.
+
+Required properties:
+- compatible: Must be "img,pistachio-pdm"
+- clocks: phandle to input PDM clock
+- clock-names: Must include the following entry:
+  - pdm: input clock to pdm block.
+- img,cr-periph: Must contain a phandle to the peripheral control
+  syscon node which contains PDM control registers.
+- #pdm-cells: Must be 2.
+- The first cell is the PDM channel number (valid values: 0, 1, 2, 3)
+- The second cell is 12-bit pulse-in value
+
+Specifying PDM information for devices
+======================================
+
+1. PDM User nodes
+
+PDM properties should be named "pdms". The exact meaning of each pdms property
+is described above.
+
+	pdm-specifier : array of #pdm-cells specifying the given PDM
+						(controller specific)
+
+The following example could be used to describe a PDM-based backlight device:
+
+	pdm: pdm {
+		#pdm-cells = <2>;
+	};
+
+	[...]
+
+	bl: backlight {
+		pdms = <&pdm 2 0>;
+	};
+
+pdm-specifier typically encodes the chip-relative PDM channel number and the
+12-bit pulse-in value.
+
+2. PDM Controller nodes
+
+PDM controller nodes must specify the number of cells used for the specifier
+using the '#pdm-cells' property.
+
+An example PDM controller might look like this:
+
+Example:
+	pdm: pdm@18148000 {
+		compatible = "img,pistachio-pdm";
+		clocks = <&pdm_clk>;
+		clk-names = "pdm";
+		img,cr-periph = <&cr_periph>;
+		#pdm-cells = <2>;
+	};
-- 
1.7.0.4