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Supporting SPI in i.MX RT Linux BSP

Supporting SPI in i.MX RT Linux BSP

1. Overview

This project provides support for the LPSPI controller of the i.MX RT1170 processor in the Linux BSP.

NOTE: The SPI interface is not supported for the MaaXBoard-RT as of BSP release 3.3.0. The support will be implemented in future releases of the BSP.

2. Requirements

2.1. Detailed Requirements

The following are the requirements for this project:

  1. Provide a Linux demo project combining all the requirements in this project.

  2. Provide support for the i.MX RT1170 LPSPI controller in Linux.

  3. Provide support for the raw access to the SPI device from user space.

  4. Provide support for the standard Linux SPI Flash interface.

2.2. Detailed Non-Requirements

The following are the non-requirements for this project that may otherwise not be obvious:

  • None

3. Design

3.1. Detailed Design

3.1.1.
Design: Demo Project

This project will enable the required functionality in the Linux configuration ("embedded project") called rootfs, which resides in a projects/rootfs directory, relative to the top of the Linux i.MX RT1170 installation.

3.1.2.
Design: Linux LPSPI Device Driver

In the i.MXRT1170 SoC, the LPSPI controller is compatible with the same controller of some other SoCs from the i.MX family, so the existing spi-fsl-lpspi.c driver in the Linux sources, which was initially added to support SPI in the i.MX7ULP SoC, will be used to support the LPSPI controller of the i.MXRT1170 SoC.

To enable the driver, the standard CONFIG_SPI along with the CONFIG_SPI_FSL_LPSPI options will be defined in the kernel defconfig file.

In addition to the kernel defconfig, the user must configure the LPSPI controller in DTS. Refer to https://www.kernel.org/doc/Documentation/devicetree/bindings/spi/spi-controller.yaml for details on format of the SPI nodes.

The DTS nodes for all 6 instances of the i.MXRT1170 LPSPI controller will be predefined in arch/arm/boot/dts/imxrt1170.dtsi. The clock driver for the i.MXRT1170 SoC will be updated to support the LPSPI clocks. Interrupts and clocks will be defined in the DTS nodes according to the processor reference manual. All controllers will be configured to use DMA. All the SPI nodes in the .dtsi file will be disabled by default.

Final tuning of the kernel run-time configuration, such as defining the pinctrl settings for a custom connection of an SPI device to the LPSPI controller, defining the chip-select signal, customizing the clocks etc, will be done in the user DTS file.

This project will provide an example for configuring the LPSPI1 controller. On the IMXRT1170-EVK board there is a 512KB SPI Flash device connected to this controller. The controller will be defined in the rootfs.dts.IMXRT117X_NXPEVK file as follows:

&lpspi1 { pinctrl-names = "default"; pinctrl-0 = <&pinctrl_lpspi1>; status = "okay"; assigned-clocks = <&clks IMXRT1170_CLK_ROOT_LPSPI1>; assigned-clock-parents = <&clks IMXRT1170_CLK_PLL3_PFD2>; assigned-clock-rates = <90000000>; cs-gpios = <&gpio9 28 GPIO_ACTIVE_LOW>; ... }; ... &iomuxc { ... pinctrl_lpspi1: lpspi1grp { fsl,pins = < IOMUXC_GPIO_AD_28_LPSPI1_SCK (MXRT1170_PAD_DSE) IOMUXC_GPIO_AD_29_GPIO9_IO28 (MXRT1170_PAD_DSE) IOMUXC_GPIO_AD_30_LPSPI1_SOUT (MXRT1170_PAD_DSE) IOMUXC_GPIO_AD_31_LPSPI1_SIN (MXRT1170_PAD_DSE) >; }; };

This example assigns the i.MXRT1170 pinctrl PADs GPIO_AD_28, GPIO_AD_29, GPIO_AD_30 and GPIO_AD_31 to the LPSPI1 controller and selects the LPSPI1_SCK, GPIO, LPSPI1_SOUT and LPSPI1_SIN functions for these PADs (refer to the board schematics and to the processor reference manual for details on possible IOMUXC configurations).

The example redefines the source for the root clock of the LPSPI1 to PLL3_PFD2. Divider of the root clock is set to generate an 90MHz output frequency (refer to the processor reference manual for details on possible CCM configurations).

The single chip-select is configured to the GPIO9 28 signal in the example.

3.1.3.
Design: Raw SPI Device Access

Linux provides a special spidev device driver to allow raw accesses to SPI devices from the user space: https://www.kernel.org/doc/Documentation/spi/spidev.

The standard Linux CONFIG_SPI_SPIDEV option will be defined in the kernel defconfig file to enable the spidev driver. The universal compatibility string linux,spidev will be added to the spidev driver so that it can be used in the project DTS.

The following changes will be made to rootfs.dts.IMXRT117X_NXPEVK to link the SPI Flash on the LPSPI1 controller to the spidev Linux device:

#define LPSPI_USE_SPIDEV &lpspi1 { ... #if defined(LPSPI_USE_SPIDEV) spidev: spidev@0 { status = "okay"; compatible = "linux,spidev"; spi-max-frequency = <10000000>; reg = <0>; }; ... #endif };

Note that the spidev sub-node is defined under the #if defined(LPSPI_USE_SPIDEV) condition. This is due to the fact that this projects also provides an alternative way to access the same SPI Flash via the Linux MTD interface (refer to the section below), so that the user can switch between 2 interfaces: raw spidev or MTD, by defining or un-defining the LPSPI_USE_SPIDEV pre-processor macro in the DTS file.

The following test program spidev_flash will be included to the project root file system as an example on how to read the Flash ID of an SPI Flash device from the user-space applications:

/* * Sample application that makes use of the SPIDEV interface * to access an SPI slave device. Specifically, this sample * reads a Device ID of a JEDEC-compliant SPI Flash device. */ #include <stdio.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> #include <sys/ioctl.h> #include <linux/types.h> #include <linux/spi/spidev.h> #include <stdint.h> #include <stdio.h> #include <string.h> #include <errno.h> int main(int argc, char **argv) { char *name; int fd; struct spi_ioc_transfer xfer[2]; unsigned char buf[32], *bp; int len, status; name = argv[1]; fd = open(name, O_RDWR); if (fd < 0) { perror("open"); return 1; } memset(xfer, 0, sizeof xfer); memset(buf, 0, sizeof buf); len = sizeof buf; /* * Send a GetID command */ buf[0] = 0x9f; len = 6; xfer[0].tx_buf = (unsigned long)buf; xfer[0].len = 1; xfer[1].rx_buf = (unsigned long) buf; xfer[1].len = 6; status = ioctl(fd, SPI_IOC_MESSAGE(2), xfer); if (status < 0) { perror("SPI_IOC_MESSAGE"); return -1; } printf("response(%d): ", status); for (bp = buf; len; len--) printf("%02x ", *bp++); printf("\n"); return 0; }

3.1.4.
Design: Standard Linux MTD interface to the SPI Flash

The standard interface to the SPI Flash in Linux is the Memory Technology Device (MTD), on top of which the Flash file system such as UBIFS or JFFS2 is usually used.

The following options will be enabled in the project kernel defconfig file to enable support for the MTD interface and the JFFS2 file system: CONFIG_MTD, CONFIG_MTD_BLOCK, CONFIG_MTD_SPI_NOR and CONFIG_JFFS2_FS.

The flash node will be defined in the DTS as follows:

#define LPSPI_USE_SPIDEV /* uncomment the following line to enable SPI Flash support via the Linux MTD interface */ // #undef LPSPI_USE_SPIDEV &lpspi1 { ... #if defined(LPSPI_USE_SPIDEV) ... #else flash0: mx25l400@0 { reg = <0>; #address-cells = <1>; #size-cells = <1>; compatible = "jedec,spi-nor"; spi-max-frequency = <10000000>; partition@0 { label = "data"; reg = <0x0 0x80000>; }; }; #endif };

Note that the SPI Flash is configured for the spidev driver by default. To enable access to the SPI Flash via MTD, the user must un-define the LPSPI_USE_SPIDEV macro in rootfs.dts.IMXRT117X_NXPEVK and rebuild the project.

3.2. Effect on Related Products

This project makes the following updates in the related products:

  • None

3.3. Changes to User Documentation

This project updates the following user documents:

  • None

3.4. Alternative Design

The following alternative design approaches were considered by this project but then discarded for some reason:

  • None

4. Test Plan

4.1. Secure Download Area