参考
- linux_5.10/Documentation/spi/spi-summary.rst
概念
工作原理
SPI 请求将提交至IO对列。这些请求按照“先进先出(FIFO)”原则执行，在完成后将通过回调方式告知。 当然，也有一些简单的异步封装回调方法，包含发送命令并接收应答的一类接口。
两种SPI驱动
Controller drivers ...
此类驱动的对象为SOC片上的SPI控制器，这些控制器通常支持“Master”与“Slave”角色切换。 此类驱动常直接访问硬件寄存器并使用DMA来提高数据传递效率，或许也可以通过CPU控制数据的每一位来控制可编程GPIO管脚。
Protocol drivers ...
此类驱动的对象为SOC片外接的SPI设备，这些设备以“Master”或“Slave”角色接入SPI控制器,进而完成数据的传输。 在SPI驱动之上，可能被具象化为MTD、Audio等设备接入更上一级的子系统。
数据结构
struct spi_device 结构体是两种驱动的基类。
#---- linux_5.10/include/linux/spi/spi.h
struct spi_device {
struct device dev;
struct spi_controller *controller;
struct spi_controller *master; /* compatibility layer */
...
框架
input layer, ALSA, networking, MTD, the character device framework, or other Linux subsystems.
Messages
If you like, spi_message_alloc() and spi_message_free() convenience
内存管理
SPI设备必须管理以下两种类型内存：
-
I/O 数据；
-
spi_message\spi_transfer数据； 可以使用spi_message_alloc()、spi_message_free()代为管理。
示例
设备
板级静态定义
Master
struct platform_device, 基于平台设备开发;
路径：arch/.../mach-*/board-*.c:
#include <mach/spi.h> /* for mysoc_spi_data */
/* if your mach-* infrastructure doesn't support kernels that can
* run on multiple boards, pdata wouldn't benefit from "__init".
*/
static struct mysoc_spi_data pdata __initdata = { ... };
static __init board_init(void)
{
...
/* this board only uses SPI controller #2 */
mysoc_register_spi(2, &pdata);
...
}
#include <mach/spi.h>
static struct platform_device spi2 = { ... };
void mysoc_register_spi(unsigned n, struct mysoc_spi_data *pdata)
{
struct mysoc_spi_data *pdata2;
pdata2 = kmalloc(sizeof *pdata2, GFP_KERNEL);
*pdata2 = pdata;
...
if (n == 2) {
spi2->dev.platform_data = pdata2;
register_platform_device(&spi2);
/* also: set up pin modes so the spi2 signals are
* visible on the relevant pins ... bootloaders on
* production boards may already have done this, but
* developer boards will often need Linux to do it.
*/
}
...
}
Slave
文件：arch/.../mach-*/board-*.c：
static struct ads7846_platform_data ads_info = {
.vref_delay_usecs = 100,
.x_plate_ohms = 580,
.y_plate_ohms = 410,
};
static struct spi_board_info spi_board_info[] __initdata = {
{
.modalias = "ads7846",
.platform_data = &ads_info,
.mode = SPI_MODE_0,
.irq = GPIO_IRQ(31),
.max_speed_hz = 120000 /* max sample rate at 3V */ * 16,
.bus_num = 1,
.chip_select = 0,
},
};
spi_register_board_info(spi_board_info, ARRAY_SIZE(spi_board_info));
DTS动态定义
Master
#---- build/boards/default/dts/cv181x/cv181x_base.dtsi
/ {
spi3:spi3@041B0000 {
interrupts = <57 IRQ_TYPE_LEVEL_HIGH>;
interrupt-parent = <&plic0>;
};
...
Slave
-
独占总线
#---- build/boards/default/dts/cv181x/cv181x_asic_bga.dtsi &spi3 { status = "okay"; num-cs = <1>; spidev@0 { compatible = "rohm,dh2228fv"; spi-max-frequency = <1000000>; reg = <0>; }; }; #---- build/boards/cv181x/cv1813h_milkv_duos_sd/dts_riscv/cv1813h_milkv_duos_sd.dts &spi3 { status = "okay"; spidev@0 { status = "okay"; }; }; -
多设备
参考内核文档：
- linux_5.10/Documentation/devicetree/bindings/spi/spi-bus.txt；
- linux_5.10/arch/arm/boot/dts/imx6ul-imx6ull-opos6uldev.dtsi
#---- linux_5.10/arch/arm/boot/dts/imx6ull-opos6uldev.dts /dts-v1/; #include "imx6ull-opos6ul.dtsi" # 1 # include "imx6ul.dtsi" # 1.1 #include "imx6ul-imx6ull-opos6uldev.dtsi" # 2 / { model = "Armadeus Systems OPOS6UL SoM (i.MX6ULL) on OPOS6ULDev board"; compatible = "armadeus,imx6ull-opos6uldev", "armadeus,imx6ull-opos6ul", "fsl,imx6ull"; }; #1.1- linux_5.10/arch/arm/boot/dts/imx6ul.dtsi / { ... soc { ... aips1: bus@2000000 { ... spba-bus@2000000 { ... ecspi4: spi@2014000 { #address-cells = <1>; #size-cells = <0>; compatible = "fsl,imx6ul-ecspi", "fsl,imx51-ecspi"; reg = <0x02014000 0x4000>; interrupts = <GIC_SPI 34 IRQ_TYPE_LEVEL_HIGH>; clocks = <&clks IMX6UL_CLK_ECSPI4>, <&clks IMX6UL_CLK_ECSPI4>; clock-names = "ipg", "per"; dmas = <&sdma 9 7 1>, <&sdma 10 7 2>; dma-names = "rx", "tx"; status = "disabled"; }; #2--- linux_5.10/arch/arm/boot/dts/imx6ul-imx6ull-opos6uldev.dtsi &ecspi4 { pinctrl-names = "default"; pinctrl-0 = <&pinctrl_ecspi4>; num-cs = 2; cs-gpios = <&gpio4 9 GPIO_ACTIVE_LOW>, <&gpio4 3 GPIO_ACTIVE_LOW>; status = "okay"; spidev0: spi@0 { compatible = "spidev"; reg = <0>; spi-max-frequency = <5000000>; }; spidev1: spi@1 { compatible = "spidev"; reg = <1>; spi-max-frequency = <5000000>; }; };
总结
spi-max-frequency，多通道时，需要定义设备允许的最大速率；---- 待确认；
驱动
spi_busnum_to_master(), 查找目标SPI控制器；spi_new_device(), 创建;spi_unregister_device()销毁；
SPI Controller Driver
struct spi_master *master;
struct CONTROLLER *c;
master = spi_alloc_master(dev, sizeof *c);
if (!master)
return -ENODEV;
c = spi_master_get_devdata(master);
spi_[un]register_master()注册至系统；
master操作集
master->setup(struct spi_device *spi), clock rate, SPI mode, and word sizes.master->cleanup(struct spi_device *spi), 清除之前由spi_device.controller_state锁定的状态； ...master->transfer_one_message(struct spi_master *master, struct spi_message *mesg), 发送一个mesg；
SPI Protocol Driver
static int CHIP_probe(struct spi_device *spi)
{
struct CHIP *chip;
struct CHIP_platform_data *pdata;
/* assuming the driver requires board-specific data: */
pdata = &spi->dev.platform_data;
if (!pdata)
return -ENODEV;
/* get memory for driver's per-chip state */
chip = kzalloc(sizeof *chip, GFP_KERNEL);
if (!chip)
return -ENOMEM;
spi_set_drvdata(spi, chip);
... etc
return 0;
}
static struct spi_driver CHIP_driver = {
.driver = {
.name = "CHIP",
.owner = THIS_MODULE,
.pm = &CHIP_pm_ops,
},
.probe = CHIP_probe,
.remove = CHIP_remove,
};
spi_setup(),
属性
spi_message.is_dma_mapped，
调试
sys节点
/sys/bus/spi/devices/spiB.C总线B，设备C, 都是从0开始编号；/sys/class/spi_master/spiBspi_master类，总线B；/sys/class/spi_slave/spiB
备注
master->transfer(struct spi_device *spi, struct spi_message *message),- 已经被弃用；
- 可以打断IO对列，提前发送；