Custom CMA reserved memory on i.MX8MM mini

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Custom CMA reserved memory on i.MX8MM mini

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matt67
Contributor III

Hi there,

I have a custom design with 1GB of RAM on i.MX8MM however the dtsi file is setting the shared-dma-pool with a quiet huge size.

  /* global autoconfigured region for contiguous allocations */
  linux,cma {
   compatible = "shared-dma-pool";
   reusable;
   size = <0 0x28000000>;
   alloc-ranges = <0 0x40000000 0 0x60000000>;
   linux,cma-default;
  };

I don't have video processing, how could I decrease it to its minimal value in a good way and with which values ?

Thank you

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b36401
NXP Employee
NXP Employee

It is application dependent.
CMA is required for DMA operations.
So you need to estimate how many buffers is required for the interfacing (SD card, camera, LCD, etc).
Alctually we did not measure the minimum of CMA.

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matt67
Contributor III

Thanks Victor. Can you explain me the alloc-range property. Is that <address, size, address size > like binding documentation tells? So why overlapping? 

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b36401
NXP Employee
NXP Employee

Here is a documentation regardign to device tree usage:
https://elinux.org/Device_Tree_Usage

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