FROMLIST: DT: pdm: Add binding document for IMG PDM DAC

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

(picked from https://patchwork.ozlabs.org/patch/426342/)

BUG=None
TEST=Tested on Pistachio BuB

Change-Id: I19a147794ec06c7cc08f7e7c5089cbcfad0e44a1
Signed-off-by: Naidu Tellapati <Naidu.Tellapati@imgtec.com>
Signed-off-by: Arul Ramasamy <Arul.Ramasamy@imgtec.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>

1 files changed, 54 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/misc/img-pdm.txt b/Documentation/devicetree/bindings/misc/img-pdm.txt
new file mode 100644
index 00000000000..96fde23a6cd
--- /dev/null
+++ b/Documentation/devicetree/bindings/misc/img-pdm.txt
@@ -0,0 +1,54 @@
+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>;
+	};