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1 | *** Memory binding *** | ||
2 | |||
3 | The /memory node provides basic information about the address and size | ||
4 | of the physical memory. This node is usually filled or updated by the | ||
5 | bootloader, depending on the actual memory configuration of the given | ||
6 | hardware. | ||
7 | |||
8 | The memory layout is described by the following node: | ||
9 | |||
10 | / { | ||
11 | #address-cells = <(n)>; | ||
12 | #size-cells = <(m)>; | ||
13 | memory { | ||
14 | device_type = "memory"; | ||
15 | reg = <(baseaddr1) (size1) | ||
16 | (baseaddr2) (size2) | ||
17 | ... | ||
18 | (baseaddrN) (sizeN)>; | ||
19 | }; | ||
20 | ... | ||
21 | }; | ||
22 | |||
23 | A memory node follows the typical device tree rules for "reg" property: | ||
24 | n: number of cells used to store base address value | ||
25 | m: number of cells used to store size value | ||
26 | baseaddrX: defines a base address of the defined memory bank | ||
27 | sizeX: the size of the defined memory bank | ||
28 | |||
29 | |||
30 | More than one memory bank can be defined. | ||
31 | |||
32 | |||
33 | *** Reserved memory regions *** | ||
34 | |||
35 | In /memory/reserved-memory node one can create child nodes describing | ||
36 | particular reserved (excluded from normal use) memory regions. Such | ||
37 | memory regions are usually designed for the special usage by various | ||
38 | device drivers. A good example are contiguous memory allocations or | ||
39 | memory sharing with other operating system on the same hardware board. | ||
40 | Those special memory regions might depend on the board configuration and | ||
41 | devices used on the target system. | ||
42 | |||
43 | Parameters for each memory region can be encoded into the device tree | ||
44 | with the following convention: | ||
45 | |||
46 | [(label):] (name) { | ||
47 | compatible = "linux,contiguous-memory-region", "reserved-memory-region"; | ||
48 | reg = <(address) (size)>; | ||
49 | (linux,default-contiguous-region); | ||
50 | }; | ||
51 | |||
52 | compatible: one or more of: | ||
53 | - "linux,contiguous-memory-region" - enables binding of this | ||
54 | region to Contiguous Memory Allocator (special region for | ||
55 | contiguous memory allocations, shared with movable system | ||
56 | memory, Linux kernel-specific). | ||
57 | - "reserved-memory-region" - compatibility is defined, given | ||
58 | region is assigned for exclusive usage for by the respective | ||
59 | devices. | ||
60 | |||
61 | reg: standard property defining the base address and size of | ||
62 | the memory region | ||
63 | |||
64 | linux,default-contiguous-region: property indicating that the region | ||
65 | is the default region for all contiguous memory | ||
66 | allocations, Linux specific (optional) | ||
67 | |||
68 | It is optional to specify the base address, so if one wants to use | ||
69 | autoconfiguration of the base address, '0' can be specified as a base | ||
70 | address in the 'reg' property. | ||
71 | |||
72 | The /memory/reserved-memory node must contain the same #address-cells | ||
73 | and #size-cells value as the root node. | ||
74 | |||
75 | |||
76 | *** Device node's properties *** | ||
77 | |||
78 | Once regions in the /memory/reserved-memory node have been defined, they | ||
79 | may be referenced by other device nodes. Bindings that wish to reference | ||
80 | memory regions should explicitly document their use of the following | ||
81 | property: | ||
82 | |||
83 | memory-region = <&phandle_to_defined_region>; | ||
84 | |||
85 | This property indicates that the device driver should use the memory | ||
86 | region pointed by the given phandle. | ||
87 | |||
88 | |||
89 | *** Example *** | ||
90 | |||
91 | This example defines a memory consisting of 4 memory banks. 3 contiguous | ||
92 | regions are defined for Linux kernel, one default of all device drivers | ||
93 | (named contig_mem, placed at 0x72000000, 64MiB), one dedicated to the | ||
94 | framebuffer device (labelled display_mem, placed at 0x78000000, 8MiB) | ||
95 | and one for multimedia processing (labelled multimedia_mem, placed at | ||
96 | 0x77000000, 64MiB). 'display_mem' region is then assigned to fb@12300000 | ||
97 | device for DMA memory allocations (Linux kernel drivers will use CMA is | ||
98 | available or dma-exclusive usage otherwise). 'multimedia_mem' is | ||
99 | assigned to scaler@12500000 and codec@12600000 devices for contiguous | ||
100 | memory allocations when CMA driver is enabled. | ||
101 | |||
102 | The reason for creating a separate region for framebuffer device is to | ||
103 | match the framebuffer base address to the one configured by bootloader, | ||
104 | so once Linux kernel drivers starts no glitches on the displayed boot | ||
105 | logo appears. Scaller and codec drivers should share the memory | ||
106 | allocations. | ||
107 | |||
108 | / { | ||
109 | #address-cells = <1>; | ||
110 | #size-cells = <1>; | ||
111 | |||
112 | /* ... */ | ||
113 | |||
114 | memory { | ||
115 | reg = <0x40000000 0x10000000 | ||
116 | 0x50000000 0x10000000 | ||
117 | 0x60000000 0x10000000 | ||
118 | 0x70000000 0x10000000>; | ||
119 | |||
120 | reserved-memory { | ||
121 | #address-cells = <1>; | ||
122 | #size-cells = <1>; | ||
123 | |||
124 | /* | ||
125 | * global autoconfigured region for contiguous allocations | ||
126 | * (used only with Contiguous Memory Allocator) | ||
127 | */ | ||
128 | contig_region@0 { | ||
129 | compatible = "linux,contiguous-memory-region"; | ||
130 | reg = <0x0 0x4000000>; | ||
131 | linux,default-contiguous-region; | ||
132 | }; | ||
133 | |||
134 | /* | ||
135 | * special region for framebuffer | ||
136 | */ | ||
137 | display_region: region@78000000 { | ||
138 | compatible = "linux,contiguous-memory-region", "reserved-memory-region"; | ||
139 | reg = <0x78000000 0x800000>; | ||
140 | }; | ||
141 | |||
142 | /* | ||
143 | * special region for multimedia processing devices | ||
144 | */ | ||
145 | multimedia_region: region@77000000 { | ||
146 | compatible = "linux,contiguous-memory-region"; | ||
147 | reg = <0x77000000 0x4000000>; | ||
148 | }; | ||
149 | }; | ||
150 | }; | ||
151 | |||
152 | /* ... */ | ||
153 | |||
154 | fb0: fb@12300000 { | ||
155 | status = "okay"; | ||
156 | memory-region = <&display_region>; | ||
157 | }; | ||
158 | |||
159 | scaler: scaler@12500000 { | ||
160 | status = "okay"; | ||
161 | memory-region = <&multimedia_region>; | ||
162 | }; | ||
163 | |||
164 | codec: codec@12600000 { | ||
165 | status = "okay"; | ||
166 | memory-region = <&multimedia_region>; | ||
167 | }; | ||
168 | }; | ||