[Add] 新增SPI驱动 开发说明

spi/ReadMe.md

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+
+
+
+## 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。
+
+```c
+#---- 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`:
+```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);
+		...
+	}
+```
+
+```c
+	#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`：
+```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,
+		},
+	};
+```
+
+```c
+	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
+
+```c
+	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
+
+```c
+	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；