Supporting SPI in the Linux i.MX RT10XX BSP
This is an add-on product that installs on top of the Linux BSP for the NXP i.MX RT10XX EVK board. It must be purchased separately from the Linux BSP product.
1. Overview
This document describes how to support for the LPSPI controller of the i.MX RT10XX processor in the Linux BSP.
2. Requirements
2.1. Detailed Requirements
The following are the requirements for this project:
Provide a Linux demo project combining all the requirements in this project.
Rationale: Needed to let Customer integrate results of this project into target embedded application.
Implementation: Section: "Design: Demo project".
Test: Section: "Test Plan: Demo Project".
Provide support for the i.MX RT1050 LPSPI controller in Linux.
Rationale: Explicit Customer requirement.
Implementation: Section: "Design: Linux LPSPI Device Driver".
Test: Section: "Test Plan: Linux LPSPI Driver".
Provide support for the raw access to the SPI device from user space.
Rationale: Explicit Customer requirement.
Implementation: Section: "Design: Raw SPI Device Access".
Test: Section: "Test Plan: Raw SPI Device Access".
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 RT1050 or i.MX RT1060 installation.
3.1.2. Design: Linux LPSPI Device Driver
In the i.MXRT1050/1060 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.MXRT1050/1060 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 4 instances of the i.MXRT1050/1060 LPSPI controller will be predefined in arch/arm/boot/dts/nxp/imx/imxrt1050.dtsior in arch/arm/boot/dts/nxp/imx/imxrt1060.dtsi. The clock driver for the i.MXRT1050/1060 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 the 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. There are no SPI devices on the IMXRT1050/1060-EVKB board connected to the LPSPI controller, so external SPI Flash connected via the SD TF to TF Flexible Card Extension cable will be used to demonstrate reading the SPI device registers.
The lpspi1 node will be configured in the rootfs.dts.IMXRT105X_NXPEVK or in the rootfs.dts.IMXRT106X_NXPEVK file as follows:
&lpspi1 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_lpspi1>;
status = "okay";
cs-gpios = <&gpio3 13 GPIO_ACTIVE_LOW>;
num-chipselects = <1>;
...
};
&iomuxc {
...
pinctrl_lpspi1: lpspi1grp {
fsl,pins = <
MXRT1050_IOMUXC_GPIO_SD_B0_00_LPSPI1_SCK MXRT10XX_PAD_CFG_SPI
MXRT1050_IOMUXC_GPIO_SD_B0_02_LPSPI1_SDO MXRT10XX_PAD_CFG_SPI
MXRT1050_IOMUXC_GPIO_SD_B0_03_LPSPI1_SDI MXRT10XX_PAD_CFG_SPI
/* CS#1 (SPI Flash) */
MXRT1050_IOMUXC_GPIO_SD_B0_01_GPIO3_IO13 MXRT10XX_PAD_CFG_GPIO
>;
};
};This example assigns the i.MXRT1050/1060 pinctrl PADs GPIO_SD_B0_00, GPIO_SD_B0_01, GPIO_SD_B0_02 and GPIO_SD_B0_03 to the LPSPI1 controller and selects the LPSPI1_SCK, GPIO, LPSPI1_SDO and LPSPI1_SDI functions for these PADs (refer to the board schematics and to the processor reference manual for details on possible IOMUXC configurations).
The single chip-select is configured to the GPIO3 13 signal in the example.
Due to the fact that the GPIO_SD_B0_00, GPIO_SD_B0_01, GPIO_SD_B0_02 and GPIO_SD_B0_03 PADs are used for the SD card controller, the changes for LPSPI1 will be provided under the #if defined(SPI_FLASH_ON_LPSPI1) condition. If the SPI_FLASH_ON_LPSPI1 is defined in DTS, the SD-card controller will be disabled.
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.IMXRT105X_NXPEVK to link an external SPI Flash to the spidev Linux device:
&lpspi1 {
...
#if defined(LPSPI_USE_SPIDEV)
spidev: spidev@0 {
status = "okay";
compatible = "linux,spidev";
spi-max-frequency = <33000000>;
reg = <0>;
};
...
#endif
};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;
} 3.2. 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
The downloadable materials developed by this project are available from a secure Web page on the Emcraft Systems web site. Specifically, proceed to the following URL to download the software materials:
For the i.MX RT1050 BSP (release 3.0.4):
The page is protected as follows:
Login: CONTACT EMCRAFT
Password: CONTACT EMCRAFT
For the i.MX RT1050 BSP (release 3.1.0):