topic Re: Where to configure CMA memory in i.MX Processors

Where to configure CMA memory

erlend_eriksen — Fri, 28 Feb 2020 15:17:52 GMT

It is possible to reserve cma memory by using the CONFIG_CMA_SIZE_MBYTES in the kernel, as mentioned here: How does imx6qp increase cma memory

However, it is also possible to configure it in the device tree, as mentioned here: Custom CMA reserved memory on i.MX8MM mini

Question 1:

What is the difference between setting CMA memory in the kernel menuconfig and in the device tree?

Question 2:

What will happen if I use both options?

Question 3:

Which one should I use if my goal is to reserve enough memory for the VPU?

Re: Where to configure CMA memory

igorpadykov — Mon, 02 Mar 2020 07:52:25 GMT

Hi Erlend

>Question 1: What is the difference between setting CMA memory in the kernel menuconfig

>and in the device tree?

Kernel config option CONFIG_CMA_SIZE_MBYTES sets the default CMA size.

Note some kernels (for example old) do not support device tree.

Additional description can be found on

Changing memory size reserved for CMA · alliedvision/documentation Wiki · GitHub

>Question 2: What will happen if I use both options?

if kernel supports device tree, setting CMA memory in the device tree will be used.

>Question 3: Which one should I use if my goal is to reserve enough memory for the VPU?

one can use device tree settings for i.MX6 Sabre boards from nxp linux

source.codeaurora.org/external/imx/linux-imx repository

dts\boot\arm\arch - linux-imx - i.MX Linux kernel

Linux documentation

i.MX Software and Development Tools | NXP

Best regards
igor
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Re: Where to configure CMA memory

864535720 — Sat, 14 Mar 2020 07:31:26 GMT

Hi,igorpadykov:

I found CONFIG_CMA_SIZE_MBYTES = 0 on the board of IMX7D. I set CONFIG_CMA_SIZE_MBYTES = 256 through make menuconfig. After I set it, I found that the kernel crashed after running for 1 day. I modified it back to CONFIG_CMA_SIZE_MBYTES = 0, the kernel will not crash, but it will always print alloc_contig_range: [ac0c0, ac0d4) PFNs busy information.
How do I set CONFIG_CMA_SIZE_MBYTES?