Linux_Drivers/spi/ReadMe.md

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

静态定义

板级设备

Master

"struct platform_device" 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));

非静态定义

使用spi_busnum_to_master()查找目标SPI控制器； 使用spi_new_device()创建; 使用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；

接口

• 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 struct spi_driver CHIP_driver = {
		.driver = {
			.name		= "CHIP",
			.owner		= THIS_MODULE,
			.pm		= &CHIP_pm_ops,
		},

		.probe		= CHIP_probe,
		.remove		= CHIP_remove,
	};


	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;
	}

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/spiB spi_master类，总线B；
• /sys/class/spi_slave/spiB

备注

• master->transfer(struct spi_device *spi, struct spi_message *message),
  1. 已经被弃用；
  2. 可以打断IO对列，提前发送；