topic Re: Custom CMA reserved memory on i.MX8MM mini in i.MX Processors

Custom CMA reserved memory on i.MX8MM mini

matt67 — Wed, 05 Feb 2020 17:38:09 GMT

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;
  };
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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

Re: Custom CMA reserved memory on i.MX8MM mini

b36401 — Thu, 06 Feb 2020 06:25:47 GMT

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.

Re: Custom CMA reserved memory on i.MX8MM mini

matt67 — Thu, 06 Feb 2020 06:40:22 GMT

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

Re: Custom CMA reserved memory on i.MX8MM mini

b36401 — Sat, 13 Jun 2020 03:47:56 GMT

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