[Add] 新增SPI驱动 开发说明
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gaoyang3513
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spi/ReadMe.md
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spi/ReadMe.md
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## 参考
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- linux_5.10/Documentation/spi/spi-summary.rst
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## 概念
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### 工作原理
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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。
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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。
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### 两种SPI驱动
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#### Controller drivers ...
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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。
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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。
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#### Protocol drivers ...
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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。
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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。
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### 数据结构
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`struct spi_device` 结构体是两种驱动的基类。
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```c
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#---- linux_5.10/include/linux/spi/spi.h
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struct spi_device {
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struct device dev;
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struct spi_controller *controller;
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struct spi_controller *master; /* compatibility layer */
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...
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```
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### 框架
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input layer, ALSA, networking, MTD, the character device framework,
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or other Linux subsystems.
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### Messages
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If you like, spi_message_alloc() and spi_message_free() convenience
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### 内存管理
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SPI设备必须管理以下两种类型内存：
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- I/O 数据；
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- spi_message\spi_transfer数据；
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可以使用spi_message_alloc()、spi_message_free()代为管理。
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## 示例
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### 静态定义
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#### 板级设备
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##### Master
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"struct platform_device"
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路径：`arch/.../mach-*/board-*.c`:
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```c
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#include <mach/spi.h> /* for mysoc_spi_data */
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/* if your mach-* infrastructure doesn't support kernels that can
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* run on multiple boards, pdata wouldn't benefit from "__init".
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*/
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static struct mysoc_spi_data pdata __initdata = { ... };
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static __init board_init(void)
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{
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...
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/* this board only uses SPI controller #2 */
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mysoc_register_spi(2, &pdata);
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...
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}
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```
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```c
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#include <mach/spi.h>
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static struct platform_device spi2 = { ... };
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void mysoc_register_spi(unsigned n, struct mysoc_spi_data *pdata)
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{
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struct mysoc_spi_data *pdata2;
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pdata2 = kmalloc(sizeof *pdata2, GFP_KERNEL);
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*pdata2 = pdata;
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...
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if (n == 2) {
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spi2->dev.platform_data = pdata2;
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register_platform_device(&spi2);
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/* also: set up pin modes so the spi2 signals are
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* visible on the relevant pins ... bootloaders on
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* production boards may already have done this, but
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* developer boards will often need Linux to do it.
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*/
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}
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...
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}
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```
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##### Slave
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文件：`arch/.../mach-*/board-*.c`：
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```c
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static struct ads7846_platform_data ads_info = {
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.vref_delay_usecs = 100,
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.x_plate_ohms = 580,
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.y_plate_ohms = 410,
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};
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static struct spi_board_info spi_board_info[] __initdata = {
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{
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.modalias = "ads7846",
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.platform_data = &ads_info,
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.mode = SPI_MODE_0,
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.irq = GPIO_IRQ(31),
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.max_speed_hz = 120000 /* max sample rate at 3V */ * 16,
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.bus_num = 1,
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.chip_select = 0,
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},
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};
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```
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```c
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spi_register_board_info(spi_board_info, ARRAY_SIZE(spi_board_info));
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```
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### 非静态定义
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使用`spi_busnum_to_master()`查找目标SPI控制器；
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使用`spi_new_device()`创建;
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使用`spi_unregister_device()`销毁；
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### SPI Controller Driver
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```c
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struct spi_master *master;
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struct CONTROLLER *c;
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master = spi_alloc_master(dev, sizeof *c);
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if (!master)
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return -ENODEV;
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c = spi_master_get_devdata(master);
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```
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- `spi_[un]register_master()`注册至系统；
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#### 接口
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- `master->setup(struct spi_device *spi)`, clock rate, SPI mode, and word sizes.
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- `master->cleanup(struct spi_device *spi)`, 清除之前由`spi_device.controller_state`锁定的状态；
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...
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- `master->transfer_one_message(struct spi_master *master, struct spi_message *mesg)`, 发送一个mesg；
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### SPI Protocol Driver
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```c
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static struct spi_driver CHIP_driver = {
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.driver = {
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.name = "CHIP",
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.owner = THIS_MODULE,
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.pm = &CHIP_pm_ops,
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},
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.probe = CHIP_probe,
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.remove = CHIP_remove,
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};
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static int CHIP_probe(struct spi_device *spi)
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{
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struct CHIP *chip;
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struct CHIP_platform_data *pdata;
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/* assuming the driver requires board-specific data: */
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pdata = &spi->dev.platform_data;
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if (!pdata)
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return -ENODEV;
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/* get memory for driver's per-chip state */
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chip = kzalloc(sizeof *chip, GFP_KERNEL);
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if (!chip)
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return -ENOMEM;
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spi_set_drvdata(spi, chip);
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... etc
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return 0;
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}
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```
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spi_setup(),
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## 属性
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- `spi_message.is_dma_mapped`，
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## 调试
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#### sys节点
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- `/sys/bus/spi/devices/spiB.C` 总线B，设备C, 都是从0开始编号；
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- `/sys/class/spi_master/spiB` spi_master类，总线B；
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- `/sys/class/spi_slave/spiB`
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## 备注
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- `master->transfer(struct spi_device *spi, struct spi_message *message)`,
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1. 已经被弃用；
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2. 可以打断IO对列，提前发送；
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