Rockchip Linux CMA Development Guide

ID: RK-GL-YF-117

Release Version: V1.0.0

Date: 2020-10-18

Security Level: □Top-Secret □Secret □Internal ■Public

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Preface

Overview

This document provides a standard template for reference. Subsequent templates will be based on this document.

Product Versions

Chip Name	Kernel Version
RK3399, RK3288, RK3368, RV1126	Linux-4.4, Linux-4.19

Intended Audience

This document (guide) is mainly applicable to the following engineers:

Technical Support Engineers

Software Development Engineers

Revision History

Version	Author	Revision Date	Description
V1.0.0	Xu Jianqun	2020-10-18	Initial version

Table of Contents

[TOC]

Memory Reservation Allocation Methods

Allocation Method 1: Reserve 16MB via menuconfig

CONFIG_DMA_CMA=y CONFIG_CMA_SIZE_MBYTES=16 CONFIG_CMA_SIZE_SEL_MBYTES=y

Allocation Method 2: Via dts reserved-memory Node

Refer to Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt technical documentation

reserved-memory {
	#address-cells = <1>;
	#size-cells = <1>;
	ranges;

	/* global autoconfigured region for contiguous allocations */
	linux,cma {
		compatible = "shared-dma-pool";
		reusable;
		size = <0x1000000>;
		alignment = <0x2000>;
		linux,cma-default;
	};
};

Memory Exclusive Allocation Methods

The above methods allocate system shared memory blocks. After multiple devices repeatedly apply for and release memory, fragmentation can occur. Some peripherals require large CMA memory blocks, and fragmentation can cause abnormal operation of these peripherals. Therefore, it is necessary to allocate dedicated memory blocks to specific devices.

Allocation Method 1: Allocated Memory Block Exists Independently, Can Be Borrowed by the System

reserved-memory {
	#address-cells = <1>;
	#size-cells = <1>;
	ranges;

	cma_region: region@88000000 {
		compatible = "shared-dma-pool";
		reusable;
		reg = <0x88000000 0x1800000>;
	};
};

The memory block allocated using this method can be assigned to a specific device via of_reserved_mem_device_init.

#include <linux/of_reserved_mem.h>
static inline int of_reserved_mem_device_init(struct device *dev)
{
	return of_reserved_mem_device_init_by_idx(dev, dev->of_node, 0);
}

Allocation Method 2: Allocated Memory Block as memblock

reserved-memory {
	#address-cells = <1>;
	#size-cells = <1>;
	ranges;

	display_reserved: framebuffer@78000000 {
		reg = <0x78000000 0x800000>;
	};
};

The allocation result can be viewed via the /sys/kernel/debug/memblock/reserved node.

The memblock ranges displayed by the node are merged and organized.

Memory blocks allocated using this method do not have kernel page management. Users should create page scale lists as needed.

console:/sys/kernel/debug/cma # cat /sys/kernel/debug/memblock/reserved
	0: 0x60004000..0x60007fff
	1: 0x60100000..0x61404a07
	2: 0x62e00000..0x62eeffff
	3: 0x68300000..0x6830d07f
...

Memory Reservation Debug Methods

Enabling CMA_DEBUG

CONFIG_CMA_DEBUGFS=y # Enable debug file system node

CONFIG_CMA_DEBUG=y # Print CMA log information

Viewing Debug Nodes

console:/sys/kernel/debug/cma # ls
cma-region@8800 cma-reserved
console:/sys/kernel/debug/cma/cma-reserved # ls
alloc    bitmap free     order_per_bit      used
base_pfn count  maxchunk

alloc: Used to allocate memory from the current CMA block, unit: pages
bitmap: Marks whether each page of the current CMA block is allocated. 1 means allocated, 0 means not allocated
free: Used to free memory from the current CMA block, unit: pages
order_per_bit: Indicates the order of pages represented by one BIT
used: Number of currently allocated pages, unit: pages
base_pfn: Page frame number of the first page in the current CMA block
maxchunk: Maximum number of contiguous free pages in the current CMA block, unit: pages

Boot-Time Memory Reservation Information

[    0.000000] Booting Linux on physical CPU 0xf00
[    0.000000] CPU: ARMv7 Processor [410fc075] revision 5 (ARMv7), cr=10c5387d
[    0.000000] CPU: div instructions available: patching division code
[    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[    0.000000] OF: fdt: Machine model: Rockchip RK3126 bnd-d708 board
[    0.000000] earlycon: uart8250 at MMIO32 0x20068000 (options '')
[    0.000000] bootconsole [uart8250] enabled
[    0.000000] Memory policy: Data cache writealloc
[    0.000000] Reserved memory: created CMA memory pool at 0x88000000, size 24 MiB
[    0.000000] OF: reserved mem: initialized node region@88000000, compatible id shared-dma-pool
[    0.000000] cma: Reserved 16 MiB at 0x9f000000
[    0.000000] On node 0 totalpages: 258560
[    0.000000] Normal zone: 1728 pages used for memmap
[    0.000000] Normal zone: 0 pages reserved
[    0.000000] Normal zone: 193024 pages, LIFO batch:63
[    0.000000] HighMem zone: 65536 pages, LIFO batch:15
[    0.000000] psci: probing for conduit method from DT.
[    0.000000] psci: PSCIv65535.65535 detected in firmware.
[    0.000000] psci: Using standard PSCI v0.2 function IDs
[    0.000000] psci: MIGRATE_INFO_TYPE not supported.
[    0.000000] psci: SMC Calling Convention v1.0
[    0.000000] percpu: Embedded 17 pages/cpu s38924 r8192 d22516 u69632
[    0.000000] pcpu-alloc: s38924 r8192 d22516 u69632 alloc=17*4096
[    0.000000] pcpu-alloc: [0] 0 [0] 1 [0] 2 [0] 3
[    0.000000] Built 1 zonelists, mobility grouping on.  Total pages: 256832
[    0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes)
[    0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes)
[    0.000000] mem auto-init: stack:off, heap alloc:off, heap free:off
[    0.000000] Memory: 960940K/1034240K available (11264K kernel code, 985K rwdata, 3180K rodata, 1024K init, 2104K bss, 32340K reserved, 40960K cma-reserved, 245024K highmem)
...

First CMA allocation success message:

[    0.000000] Reserved memory: created CMA memory pool at 0x88000000, size 24 MiB
[    0.000000] OF: reserved mem: initialized node region@88000000, compatible id shared-dma-pool

Second CMA allocation success message (system default):

[    0.000000] cma: Reserved 16 MiB at 0x9f000000

Memory Reservation Allocation Methods​

Allocation Method 1: Reserve 16MB via menuconfig​

Allocation Method 2: Via dts reserved-memory Node​

Memory Exclusive Allocation Methods​

Allocation Method 1: Allocated Memory Block Exists Independently, Can Be Borrowed by the System​

Allocation Method 2: Allocated Memory Block as memblock​

Memory Reservation Debug Methods​

Enabling CMA_DEBUG​

Viewing Debug Nodes​

Boot-Time Memory Reservation Information​