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Contributor
Contributor
528 Views
Registered: ‎08-09-2013

reserved-memory for dma or vdma, the speed is slow when use memcpy.

reserved-memory for dma or vdma, the speed is slow when use memcpy.

i used petalinux 2017.4

in the devicetree you may change the

"no-map" to "reusable", like,

reserved-memory {
#address-cells = <1>;
#size-cells = <1>;
ranges;
reserved: buffer@0x1C000000 {
no-map;

reg = <0x1C000000 0x2000000>;
};
};

to

reserved-memory {
#address-cells = <1>;
#size-cells = <1>;
ranges;
reserved: buffer@0x1C000000 {
reusable;
reg = <0x1C000000 0x2000000>;
};
};

i think it is because  the uncached memory,

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.

when i change this ,the speed is up about 6 times.

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