Introduction

Linux MTD subsystem has originally provided drivers for some SPI NOR/NAND flash models, and Realtek has made some changes to support SoC’s MCM flash. Limited by the implementation of SPI Flash controller driver, the SPI NOR/NAND flash drivers only work in user mode.

Architecture

The software architectures of SPI NOR/NAND Flash driver are illustrated in the following two figures respectively.

../../_images/nor_flash_driver_software_arch.svg

../../_images/nand_flash_driver_software_arch.svg

Implementation

The SPI NOR/NAND Flash drivers are originally implemented by Linux kernel as following files:

File	Description
<linux>/drivers/mtd/spi-nor/Kconfig	SPI NOR Flash driver Kconfig
<linux>/drivers/mtd/spi-nor/Makefile	SPI NOR Flash driver Makefile
<linux>/drivers/mtd/spi-nor/spi-nor.c	SPI NOR Flash driver implementation
<linux>/drivers/mtd/nand/spi/Kconfig	SPI NAND Flash driver Kconfig
<linux>/drivers/mtd/nand/spi/Makefile	SPI NAND Flash driver Makefile
<linux>/drivers/mtd/nand/spi/core.c	SPI NAND Flash core driver
<linux>/drivers/mtd/nand/spi/*.c	SPI NAND Flash manufacture drivers

Configuration

DTS Configuration

For NOR Flash driver, the DTS node is defined in <dts>/rtl8730e-spi-nor.dtsi.

flash0: flash@0 {
   #address-cells = <1>;
   #size-cells = <1>;
   compatible = "jedec,spi-nor";
   spi-max-frequency = <100000000>;
   reg = <0>;
   partitions {
      compatible = "fixed-partitions";
      #address-cells = <1>;
      #size-cells = <1>;
      /* Partitions */
   };
};

For NAND Flash driver, the DTS node is defined in <dts>/rtl8730e-spi-nand-128m.dtsi or <dts>/rtl8730e-spi-nand-256m.dtsi.

flash0: flash@0 {
   #address-cells = <1>;
   #size-cells = <1>;
   compatible = "spi-nand";
   spi-max-frequency = <100000000>;
   reg = <0>;
   partitions {
      compatible = "fixed-partitions";
      #address-cells = <1>;
      #size-cells = <1>;
      /* Partitions */
   };
};

The configurations are listed in the table below:

Property	Description	Configurable?
compatible	ID to match the flash driver with flash device	No
#address-cells	Address cells for flash partition child node	No
#size-cells	Size cells for flash partition child node	No
reg	Reserved	No
mode	Reserved	No
partitions	The partitions for different area at flash, user can modify the partitions’ size, lable, etc.	Yes

Note

Above DTS files will be auto selected after chip is chosen, do not change the DTS configurations if not necessary.

Build Configuration

For SPI NAND/NOR Flash:

Select Device Drivers -> Memory Technology Divece (MTD) support
Select SPI-NOR device support or SPI-NAND device support

APIs

APIs for User Space

User can access data on Flash from user space via:

C API provided by GLIBC, such as open/close/read/write functions

Refer to The GNU C Library for details.
Shell utilities provided by Busybox, such as mount/unmount/mkdir/rm comands

Refer to BusyBox for details.

APIs for Kernel Space

The SPI NAND/NOR Flash drivers provide callbacks for MTD framework, the prototypes of these callbacks are defined in <linux>/include/linux/mtd/mtd.h.

SPI NOR Flash driver provides the following callbacks:

API	Introduction
_erase	Erase the specific SPI NOR Flash region
_read	Read data from SPI NOR Flash to buffer
_write	Write data from buffer to SPI NOR Flash
_resume	Resume handler for power management
_lock	Lock specific SPI NOR Flash region
_unlock	Unlock specific SPI NOR Flash region
_is_locked	Check the specific SPI NOR Flash region is locked

Refer to SPI NOR framework for details of Linux SPI NOR framework.

SPI NAND Flash driver provides the following callbacks:

API	Introduction
_read_oob	Read data from SPI NAND Flash to buffer
_write_oob	Write data from buffer to SPI NAND Flash
_block_isbad	Check whether the SPI NAND Flash block is marked as bad block
_block_markbad	Mark the SPI NAND Flash block as bad block
_block_isreserved	Check whether the SPI NAND Flash block is reserved
_erase	Erase the specific SPI NAND Flash region
_max_bad_blocks	Get the maximum number of bad blocks on a specific SPI NAND Flash region

Refer to MTD NAND Driver Programming Interface for details of MTD NAND driver programming interfaces.