mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-12-24 20:13:39 +00:00
656d8da9d2
Commit ad7061ed74 ("doc: Move device tree bindings documentation to
doc/device-tree-bindings") moved all device tree binding documentation
to doc/device-tree-bindings directory.
The current U-Boot project still have two documentation directories:
- doc/
- Documentation/
Move all documentation and sphinx files to doc directory so all content
can be in a common place.
Signed-off-by: Breno Lima <breno.lima@nxp.com>
136 lines
4.7 KiB
Text
136 lines
4.7 KiB
Text
*** Reserved memory regions ***
|
|
|
|
Reserved memory is specified as a node under the /reserved-memory node.
|
|
The operating system shall exclude reserved memory from normal usage
|
|
one can create child nodes describing particular reserved (excluded from
|
|
normal use) memory regions. Such memory regions are usually designed for
|
|
the special usage by various device drivers.
|
|
|
|
Parameters for each memory region can be encoded into the device tree
|
|
with the following nodes:
|
|
|
|
/reserved-memory node
|
|
---------------------
|
|
#address-cells, #size-cells (required) - standard definition
|
|
- Should use the same values as the root node
|
|
ranges (required) - standard definition
|
|
- Should be empty
|
|
|
|
/reserved-memory/ child nodes
|
|
-----------------------------
|
|
Each child of the reserved-memory node specifies one or more regions of
|
|
reserved memory. Each child node may either use a 'reg' property to
|
|
specify a specific range of reserved memory, or a 'size' property with
|
|
optional constraints to request a dynamically allocated block of memory.
|
|
|
|
Following the generic-names recommended practice, node names should
|
|
reflect the purpose of the node (ie. "framebuffer" or "dma-pool"). Unit
|
|
address (@<address>) should be appended to the name if the node is a
|
|
static allocation.
|
|
|
|
Properties:
|
|
Requires either a) or b) below.
|
|
a) static allocation
|
|
reg (required) - standard definition
|
|
b) dynamic allocation
|
|
size (required) - length based on parent's #size-cells
|
|
- Size in bytes of memory to reserve.
|
|
alignment (optional) - length based on parent's #size-cells
|
|
- Address boundary for alignment of allocation.
|
|
alloc-ranges (optional) - prop-encoded-array (address, length pairs).
|
|
- Specifies regions of memory that are
|
|
acceptable to allocate from.
|
|
|
|
If both reg and size are present, then the reg property takes precedence
|
|
and size is ignored.
|
|
|
|
Additional properties:
|
|
compatible (optional) - standard definition
|
|
- may contain the following strings:
|
|
- shared-dma-pool: This indicates a region of memory meant to be
|
|
used as a shared pool of DMA buffers for a set of devices. It can
|
|
be used by an operating system to instantiate the necessary pool
|
|
management subsystem if necessary.
|
|
- vendor specific string in the form <vendor>,[<device>-]<usage>
|
|
no-map (optional) - empty property
|
|
- Indicates the operating system must not create a virtual mapping
|
|
of the region as part of its standard mapping of system memory,
|
|
nor permit speculative access to it under any circumstances other
|
|
than under the control of the device driver using the region.
|
|
reusable (optional) - empty property
|
|
- The operating system can use the memory in this region with the
|
|
limitation that the device driver(s) owning the region need to be
|
|
able to reclaim it back. Typically that means that the operating
|
|
system can use that region to store volatile or cached data that
|
|
can be otherwise regenerated or migrated elsewhere.
|
|
|
|
Linux implementation note:
|
|
- If a "linux,cma-default" property is present, then Linux will use the
|
|
region for the default pool of the contiguous memory allocator.
|
|
|
|
- If a "linux,dma-default" property is present, then Linux will use the
|
|
region for the default pool of the consistent DMA allocator.
|
|
|
|
Device node references to reserved memory
|
|
-----------------------------------------
|
|
Regions in the /reserved-memory node may be referenced by other device
|
|
nodes by adding a memory-region property to the device node.
|
|
|
|
memory-region (optional) - phandle, specifier pairs to children of /reserved-memory
|
|
|
|
Example
|
|
-------
|
|
This example defines 3 contiguous regions are defined for Linux kernel:
|
|
one default of all device drivers (named linux,cma@72000000 and 64MiB in size),
|
|
one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB), and
|
|
one for multimedia processing (named multimedia-memory@77000000, 64MiB).
|
|
|
|
/ {
|
|
#address-cells = <1>;
|
|
#size-cells = <1>;
|
|
|
|
memory {
|
|
reg = <0x40000000 0x40000000>;
|
|
};
|
|
|
|
reserved-memory {
|
|
#address-cells = <1>;
|
|
#size-cells = <1>;
|
|
ranges;
|
|
|
|
/* global autoconfigured region for contiguous allocations */
|
|
linux,cma {
|
|
compatible = "shared-dma-pool";
|
|
reusable;
|
|
size = <0x4000000>;
|
|
alignment = <0x2000>;
|
|
linux,cma-default;
|
|
};
|
|
|
|
display_reserved: framebuffer@78000000 {
|
|
reg = <0x78000000 0x800000>;
|
|
};
|
|
|
|
multimedia_reserved: multimedia@77000000 {
|
|
compatible = "acme,multimedia-memory";
|
|
reg = <0x77000000 0x4000000>;
|
|
};
|
|
};
|
|
|
|
/* ... */
|
|
|
|
fb0: video@12300000 {
|
|
memory-region = <&display_reserved>;
|
|
/* ... */
|
|
};
|
|
|
|
scaler: scaler@12500000 {
|
|
memory-region = <&multimedia_reserved>;
|
|
/* ... */
|
|
};
|
|
|
|
codec: codec@12600000 {
|
|
memory-region = <&multimedia_reserved>;
|
|
/* ... */
|
|
};
|
|
};
|