dmaengine: hidma: Add Device Tree binding

Add documentation for the Qualcomm Technologies HIDMA binding.
Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

Documentation/devicetree/bindings/dma/qcom_hidma_mgmt.txt

+Qualcomm Technologies HIDMA Management interface
+
+Qualcomm Technologies HIDMA is a high speed DMA device. It only supports
+memcpy and memset capabilities. It has been designed for virtualized
+environments.
+
+Each HIDMA HW instance consists of multiple DMA channels. These channels
+share the same bandwidth. The bandwidth utilization can be parititioned
+among channels based on the priority and weight assignments.
+
+There are only two priority levels and 15 weigh assignments possible.
+
+Other parameters here determine how much of the system bus this HIDMA
+instance can use like maximum read/write request and and number of bytes to
+read/write in a single burst.
+
+Main node required properties:
+- compatible: "qcom,hidma-mgmt-1.0";
+- reg: Address range for DMA device
+- dma-channels: Number of channels supported by this DMA controller.
+- max-write-burst-bytes: Maximum write burst in bytes that HIDMA can
+  occupy the bus for in a single transaction. A memcpy requested is
+  fragmented to multiples of this amount. This parameter is used while
+  writing into destination memory. Setting this value incorrectly can
+  starve other peripherals in the system.
+- max-read-burst-bytes: Maximum read burst in bytes that HIDMA can
+  occupy the bus for in a single transaction. A memcpy request is
+  fragmented to multiples of this amount. This parameter is used while
+  reading the source memory. Setting this value incorrectly can starve
+  other peripherals in the system.
+- max-write-transactions: This value is how many times a write burst is
+  applied back to back while writing to the destination before yielding
+  the bus.
+- max-read-transactions: This value is how many times a read burst is
+  applied back to back while reading the source before yielding the bus.
+- channel-reset-timeout-cycles: Channel reset timeout in cycles for this SOC.
+  Once a reset is applied to the HW, HW starts a timer for reset operation
+  to confirm. If reset is not completed within this time, HW reports reset
+  failure.
+
+Sub-nodes:
+
+HIDMA has one or more DMA channels that are used to move data from one
+memory location to another.
+
+When the OS is not in control of the management interface (i.e. it's a guest),
+the channel nodes appear on their own, not under a management node.
+
+Required properties:
+- compatible: must contain "qcom,hidma-1.0"
+- reg: Addresses for the transfer and event channel
+- interrupts: Should contain the event interrupt
+- desc-count: Number of asynchronous requests this channel can handle
+- iommus: required a iommu node
+
+Example:
+
+Hypervisor OS configuration:
+
+	hidma-mgmt@f9984000 = {
+		compatible = "qcom,hidma-mgmt-1.0";
+		reg = <0xf9984000 0x15000>;
+		dma-channels = <6>;
+		max-write-burst-bytes = <1024>;
+		max-read-burst-bytes = <1024>;
+		max-write-transactions = <31>;
+		max-read-transactions = <31>;
+		channel-reset-timeout-cycles = <0x500>;
+
+		hidma_24: dma-controller@0x5c050000 {
+			compatible = "qcom,hidma-1.0";
+			reg = <0 0x5c050000 0x0 0x1000>,
+			      <0 0x5c0b0000 0x0 0x1000>;
+			interrupts = <0 389 0>;
+			desc-count = <10>;
+			iommus = <&system_mmu>;
+		};
+	};
+
+Guest OS configuration:
+
+	hidma_24: dma-controller@0x5c050000 {
+		compatible = "qcom,hidma-1.0";
+		reg = <0 0x5c050000 0x0 0x1000>,
+		      <0 0x5c0b0000 0x0 0x1000>;
+		interrupts = <0 389 0>;
+		desc-count = <10>;
+		iommus = <&system_mmu>;
+	};