Documentation: Add snapshot of msm_ion.txt

ION Memory Manager (ION)

ION is a memory manager that allows for sharing of buffers between different

processes and between user space and kernel space. ION manages different

memory spaces by separating the memory spaces into "heaps". Depending on the

type of heap ION must reserve memory using the msm specific memory reservation

bindings (see Documentation/devicetree/bindings/arm/msm/memory-reserve.txt).

Required properties for Ion

- compatible: "qcom,msm-ion"

All child nodes of a qcom,msm-ion node are interpreted as Ion heap

configurations.

Required properties for Ion heaps

- reg: The ID of the ION heap.

- qcom,ion-heap-type: The heap type to use for this heap. Should be one of

  the following:

    - "SYSTEM"

    - "SYSTEM_CONTIG"

    - "CARVEOUT"

    - "CHUNK"

    - "CP"

    - "DMA"

    - "SECURE_DMA"

Optional properties for Ion heaps

- compatible: "qcom,msm-ion-reserve" This is required if memory is to be reserved

  as specified by qcom,memory-reservation-size below.

- qcom,heap-align: Alignment of start of the memory in the heap.

- qcom,heap-adjacent: ID of heap this heap needs to be adjacent to.

- qcom,memory-reservation-size: size of reserved memory for the ION heap.

- qcom,memory-reservation-type: type of memory to be reserved

(see memory-reserve.txt for information about memory reservations)

- qcom,default-prefetch-size: Base value to be used for prefetching

  optimizations. Ignored if the heap does not support prefetching.

  Will set to a reasonable default value (e.g. the maximum heap size)

  if this option is not set.

Example:

	qcom,ion {

                 compatible = "qcom,msm-ion";

                 #address-cells = <1>;

                 #size-cells = <0>;

                 qcom,ion-heap@25 {

                         reg = <25>;

                         qcom,ion-heap-type = "SYSTEM";

                 };

                 qcom,ion-heap@8 { /* CP_MM HEAP */

                         compatible = "qcom,msm-ion-reserve";

                         reg = <8>;

                         qcom,heap-align = <0x1000>;

                         linux,contiguous-region = <&secure_mem>;

                         qcom,ion-heap-type = "SECURE_DMA";

                 };

                 qcom,ion-heap@29 { /* FIRMWARE HEAP */

                         compatible = "qcom,msm-ion-reserve";

                         reg = <29>;

                         qcom,heap-align = <0x20000>;

                         qcom,heap-adjacent = <8>;

                         qcom,memory-reservation-type = "EBI1"; /* reserve EBI memory */

                         qcom,memory-reservation-size = <0xA00000>;

                         qcom,ion-heap-type = "CARVEOUT";

                 };

	};