169 строки
5.0 KiB
Plaintext
169 строки
5.0 KiB
Plaintext
*** Memory binding ***
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The /memory node provides basic information about the address and size
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of the physical memory. This node is usually filled or updated by the
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bootloader, depending on the actual memory configuration of the given
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hardware.
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The memory layout is described by the following node:
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/ {
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#address-cells = <(n)>;
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#size-cells = <(m)>;
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memory {
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device_type = "memory";
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reg = <(baseaddr1) (size1)
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(baseaddr2) (size2)
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...
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(baseaddrN) (sizeN)>;
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};
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...
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};
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A memory node follows the typical device tree rules for "reg" property:
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n: number of cells used to store base address value
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m: number of cells used to store size value
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baseaddrX: defines a base address of the defined memory bank
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sizeX: the size of the defined memory bank
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More than one memory bank can be defined.
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*** Reserved memory regions ***
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In /memory/reserved-memory node one can create child nodes describing
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particular reserved (excluded from normal use) memory regions. Such
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memory regions are usually designed for the special usage by various
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device drivers. A good example are contiguous memory allocations or
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memory sharing with other operating system on the same hardware board.
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Those special memory regions might depend on the board configuration and
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devices used on the target system.
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Parameters for each memory region can be encoded into the device tree
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with the following convention:
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[(label):] (name) {
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compatible = "linux,contiguous-memory-region", "reserved-memory-region";
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reg = <(address) (size)>;
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(linux,default-contiguous-region);
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};
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compatible: one or more of:
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- "linux,contiguous-memory-region" - enables binding of this
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region to Contiguous Memory Allocator (special region for
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contiguous memory allocations, shared with movable system
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memory, Linux kernel-specific).
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- "reserved-memory-region" - compatibility is defined, given
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region is assigned for exclusive usage for by the respective
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devices.
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reg: standard property defining the base address and size of
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the memory region
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linux,default-contiguous-region: property indicating that the region
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is the default region for all contiguous memory
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allocations, Linux specific (optional)
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It is optional to specify the base address, so if one wants to use
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autoconfiguration of the base address, '0' can be specified as a base
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address in the 'reg' property.
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The /memory/reserved-memory node must contain the same #address-cells
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and #size-cells value as the root node.
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*** Device node's properties ***
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Once regions in the /memory/reserved-memory node have been defined, they
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may be referenced by other device nodes. Bindings that wish to reference
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memory regions should explicitly document their use of the following
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property:
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memory-region = <&phandle_to_defined_region>;
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This property indicates that the device driver should use the memory
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region pointed by the given phandle.
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*** Example ***
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This example defines a memory consisting of 4 memory banks. 3 contiguous
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regions are defined for Linux kernel, one default of all device drivers
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(named contig_mem, placed at 0x72000000, 64MiB), one dedicated to the
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framebuffer device (labelled display_mem, placed at 0x78000000, 8MiB)
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and one for multimedia processing (labelled multimedia_mem, placed at
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0x77000000, 64MiB). 'display_mem' region is then assigned to fb@12300000
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device for DMA memory allocations (Linux kernel drivers will use CMA is
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available or dma-exclusive usage otherwise). 'multimedia_mem' is
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assigned to scaler@12500000 and codec@12600000 devices for contiguous
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memory allocations when CMA driver is enabled.
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The reason for creating a separate region for framebuffer device is to
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match the framebuffer base address to the one configured by bootloader,
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so once Linux kernel drivers starts no glitches on the displayed boot
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logo appears. Scaller and codec drivers should share the memory
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allocations.
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/ {
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#address-cells = <1>;
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#size-cells = <1>;
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/* ... */
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memory {
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reg = <0x40000000 0x10000000
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0x50000000 0x10000000
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0x60000000 0x10000000
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0x70000000 0x10000000>;
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reserved-memory {
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#address-cells = <1>;
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#size-cells = <1>;
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/*
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* global autoconfigured region for contiguous allocations
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* (used only with Contiguous Memory Allocator)
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*/
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contig_region@0 {
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compatible = "linux,contiguous-memory-region";
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reg = <0x0 0x4000000>;
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linux,default-contiguous-region;
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};
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/*
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* special region for framebuffer
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*/
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display_region: region@78000000 {
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compatible = "linux,contiguous-memory-region", "reserved-memory-region";
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reg = <0x78000000 0x800000>;
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};
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/*
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* special region for multimedia processing devices
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*/
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multimedia_region: region@77000000 {
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compatible = "linux,contiguous-memory-region";
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reg = <0x77000000 0x4000000>;
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};
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};
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};
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/* ... */
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fb0: fb@12300000 {
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status = "okay";
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memory-region = <&display_region>;
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};
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scaler: scaler@12500000 {
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status = "okay";
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memory-region = <&multimedia_region>;
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};
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codec: codec@12600000 {
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status = "okay";
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memory-region = <&multimedia_region>;
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};
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};
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