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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:01 EST.

1	*** Reserved memory regions ***
2	
3	Reserved memory is specified as a node under the /reserved-memory node.
4	The operating system shall exclude reserved memory from normal usage
5	one can create child nodes describing particular reserved (excluded from
6	normal use) memory regions. Such memory regions are usually designed for
7	the special usage by various device drivers.
8	
9	Parameters for each memory region can be encoded into the device tree
10	with the following nodes:
11	
12	/reserved-memory node
13	---------------------
14	#address-cells, #size-cells (required) - standard definition
15	    - Should use the same values as the root node
16	ranges (required) - standard definition
17	    - Should be empty
18	
19	/reserved-memory/ child nodes
20	-----------------------------
21	Each child of the reserved-memory node specifies one or more regions of
22	reserved memory. Each child node may either use a 'reg' property to
23	specify a specific range of reserved memory, or a 'size' property with
24	optional constraints to request a dynamically allocated block of memory.
25	
26	Following the generic-names recommended practice, node names should
27	reflect the purpose of the node (ie. "framebuffer" or "dma-pool"). Unit
28	address (@<address>) should be appended to the name if the node is a
29	static allocation.
30	
31	Properties:
32	Requires either a) or b) below.
33	a) static allocation
34	   reg (required) - standard definition
35	b) dynamic allocation
36	   size (required) - length based on parent's #size-cells
37	                   - Size in bytes of memory to reserve.
38	   alignment (optional) - length based on parent's #size-cells
39	                        - Address boundary for alignment of allocation.
40	   alloc-ranges (optional) - prop-encoded-array (address, length pairs).
41	                           - Specifies regions of memory that are
42	                             acceptable to allocate from.
43	
44	If both reg and size are present, then the reg property takes precedence
45	and size is ignored.
46	
47	Additional properties:
48	compatible (optional) - standard definition
49	    - may contain the following strings:
50	        - shared-dma-pool: This indicates a region of memory meant to be
51	          used as a shared pool of DMA buffers for a set of devices. It can
52	          be used by an operating system to instanciate the necessary pool
53	          management subsystem if necessary.
54	        - vendor specific string in the form <vendor>,[<device>-]<usage>
55	no-map (optional) - empty property
56	    - Indicates the operating system must not create a virtual mapping
57	      of the region as part of its standard mapping of system memory,
58	      nor permit speculative access to it under any circumstances other
59	      than under the control of the device driver using the region.
60	reusable (optional) - empty property
61	    - The operating system can use the memory in this region with the
62	      limitation that the device driver(s) owning the region need to be
63	      able to reclaim it back. Typically that means that the operating
64	      system can use that region to store volatile or cached data that
65	      can be otherwise regenerated or migrated elsewhere.
66	
67	Linux implementation note:
68	- If a "linux,cma-default" property is present, then Linux will use the
69	  region for the default pool of the contiguous memory allocator.
70	
71	Device node references to reserved memory
72	-----------------------------------------
73	Regions in the /reserved-memory node may be referenced by other device
74	nodes by adding a memory-region property to the device node.
75	
76	memory-region (optional) - phandle, specifier pairs to children of /reserved-memory
77	
78	Example
79	-------
80	This example defines 3 contiguous regions are defined for Linux kernel:
81	one default of all device drivers (named linux,cma@72000000 and 64MiB in size),
82	one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB), and
83	one for multimedia processing (named multimedia-memory@77000000, 64MiB).
84	
85	/ {
86		#address-cells = <1>;
87		#size-cells = <1>;
88	
89		memory {
90			reg = <0x40000000 0x40000000>;
91		};
92	
93		reserved-memory {
94			#address-cells = <1>;
95			#size-cells = <1>;
96			ranges;
97	
98			/* global autoconfigured region for contiguous allocations */
99			linux,cma {
100				compatible = "shared-dma-pool";
101				reusable;
102				size = <0x4000000>;
103				alignment = <0x2000>;
104				linux,cma-default;
105			};
106	
107			display_reserved: framebuffer@78000000 {
108				reg = <0x78000000 0x800000>;
109			};
110	
111			multimedia_reserved: multimedia@77000000 {
112				compatible = "acme,multimedia-memory";
113				reg = <0x77000000 0x4000000>;
114			};
115		};
116	
117		/* ... */
118	
119		fb0: video@12300000 {
120			memory-region = <&display_reserved>;
121			/* ... */
122		};
123	
124		scaler: scaler@12500000 {
125			memory-region = <&multimedia_reserved>;
126			/* ... */
127		};
128	
129		codec: codec@12600000 {
130			memory-region = <&multimedia_reserved>;
131			/* ... */
132		};
133	};
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