分析Linux内核中的SPI驱动源码精选

• 编码小哥
• 2023/5/17 16:50:14

一、SPI驱动框架的基本结构

在Linux内核中，SPI驱动框架的代码位于/drivers/spi目录下。该目录下的源文件主要包括以下几个：

- spi.c：SPI总线设备驱动程序

- spi-bitbang.c：位压缩SPI驱动程序

- spi-dw-dma.c：SPI DMA驱动程序

- spi-dw-mmio.c：SPI MMIO驱动程序

- spi-fsl-dspi.c：FSL DSPI驱动程序

- spi-imx.c：i.MX SPI驱动程序

- spi-pl022.c：ARM PrimeCell PL022 SPI驱动程序

- spi-s3c24xx.c：Samsung S3C24xx SPI驱动程序

- spi-tegra20-sflash.c：Nvidia SPI Flash驱动程序

- spi-ti-qspi.c：TI Quad SPI驱动程序

       这些驱动程序分别对应不同的SPI控制器。其中，spi.c是SPI驱动的核心文件，提供了SPI驱动框架的基本结构和主要函数。

二、spi.c的结构和作用

1.SPI驱动框架的初始化

SPI驱动框架的初始化主要在spi_init()函数中完成。该函数首先调用spi_bus_type_init()函数，注册SPI设备总线，然后向/sys/class下的spi_master目录中创建spi设备目录，最后调用probe_master()函数，搜索当前系统中的SPI设备并添加到bus层中。该函数的代码如下：

static int __init spi_init(void)

{

int status;

status = spi_bus_type_init();

if (status)

goto out;

status = class_register(&spi_master_class);

if (status)

goto bus_unregister;

status = spi_proc_init();

if (status)

goto class_unregister;

status = spi_gpio_register_board_info(NULL, 0);

if (status)

goto proc_cleanup;

status = spi_read_configfile();

if (status)

goto board_cleanup;

status = spi_master_probe_devices();

if (status)

goto board_cleanup;

printk(KERN_INFO "%s\n", spi_revision);

return 0;

board_cleanup:

spi_board_cleanup();

proc_cleanup:

spi_proc_cleanup();

class_unregister:

class_unregister(&spi_master_class);

bus_unregister:

spi_bus_type_exit();

out:

return status;

}

2.SPI总线设备的添加和删除

当SPI总线设备（spi_master）被发现并添加到bus层时，会自动调用spi_master_add()函数，该函数会为SPI总线设备创建一个spi_master结构体，并将其添加到bus层中。

static int spi_master_add(struct spi_master *master)

{

struct device *dev = master->dev.parent;

struct spi_controller *ctlr = master->controller;

mutex_lock(&spi_mutex);

/*

* Implementation restriction: each SPI MASTER talks with other

* devices at constant signal levels, which don't change once

* operation starts. We don't provide any synchronization

* primitives that would be necessary for anything else.

*/

if (master->num_chipselect)

dev_warn(dev, "num_chipselect should == 1 when !is_slave\n");

if (!ctlr) {

ctlr = kzalloc(sizeof(struct spi_controller), GFP_KERNEL);

if (!ctlr) {

mutex_unlock(&spi_mutex);

return -ENOMEM;

}

ctlr->master = master;

master->controller = ctlr;

master->bits_per_word_mask = 0xFFFF;

if (!spi_controller_is_slave(master)) {

ctlr->max_speed_hz = spi_max_speed_hz(&ctlr->dev, master);

ctlr->setup = spi_master_setup;

ctlr->transfer_one = spi_transfer_one;

} else {

ctlr->max_speed_hz = master->max_speed_hz;

ctlr->setup = spi_slave_setup;

ctlr->transfer_one = spi_transfer_one_slave;

}

ctlr->bits_per_word_mask = master->bits_per_word_mask;

ctlr->flags = 0;

ctlr->mode_bits = master->mode_bits;

if (spi_controller_is_slave(master)) {

ctlr->mode_bits = 0;

ctlr->flags = SPI_CONTROLLER_SLAVE;

ctlr->bus_num = spi_slave_controller_id++;

idr_init(&ctlr->idr);

} else {

ctlr->mode_bits &= ctlr->controller_ops->get_mode_bits;

ctlr->flags |= SPI_CONTROLLER_MASTER;

ctlr->bus_num = spi_master_controller_id++;

}

dev_set_drvdata(dev, master);

dev_info(dev, "registered, %s%s%s%s%s\n",

ctlr->flags & SPI_CONTROLLER_MASTER ? "master" : "",

ctlr->flags & SPI_CONTROLLER_SLAVE ? "slave" : "",

ctlr->flags & SPI_CONTROLLER_CS_WORD ? "cs-high" : "",

ctlr->flags & SPI_CONTROLLER_NEEDS_POLL ? ", polling" : "",

ctlr->mode_bits ? ", mode " : "");

 

list_add_tail(&ctlr->list, &ctlr_list);

}

mutex_unlock(&spi_mutex);

return 0;

}

当SPI总线设备从bus层中删除时，会自动调用spi_master_del()函数，该函数会删除spi_master结构体并释放相关资源。

static int spi_master_del(struct spi_master *master)

{

int my_bus_num = master->controller->bus_num;

mutex_lock(&spi_mutex);

if (my_bus_num < 0) { /* not yet attached */

mutex_unlock(&spi_mutex);

return -EINVAL;

}

if (!spi_controller_is_slave(master)) {

if (spi_master_get(master)) {

mutex_unlock(&spi_mutex);

return -EINVAL;

}

}

dev_info(&master->dev, "removed\n");

spi_controller_cleanup(master->controller);

kfree(master->controller);

return 0;

}

三、重要的数据结构和函数

1.spi_device

spi_device结构体表示一个SPI设备，包含了设备的名称、片选信号、总线速率、数据位数、SPI传输设置等信息。该结构体被定义在include/linux/spi/spi.h头文件中，其定义如下：

struct spi_device {

struct device dev;

spinlock_t regs_lock;

const struct spi_device *next;

u32 max_speed_hz;

u8 chip_select;

u8 mode;

u8 bit_order;

u16 flags;

u32 irq;

struct mutex io_mutex;

/* RT signal stuff */

struct rt_mutex rt;

struct spi_controller *controller;

};

spi_transfer结构体表示一次SPI传输，包含了传输的缓冲区、字节长度、传输设置等信息以及一个回调函数，用于在传输完成时通知上层应用程序。该结构体被定义在include/linux/spi/spi.h头文件中，其定义如下：

struct spi_transfer {

const void *tx_buf;

void *rx_buf;

unsigned len;

u32 speed_hz;

u16 delay_usecs;

u8 bits_per_word;

/* Used internally, by spi_sync() and the SPI core code */

u8 cs_change:1;

u8 do_read:1;

u8 tx_nbits:6; /* internal, for packing only */

u8 rx_nbits:6; /* internal, for packing only */

u16 rdy_for_tx:1;

u16 rdy_for_rx:1;

u16 cs_change_delay:14;

u16 large_buf:1;

u8 *tx_buf_wr;

u8 *rx_buf_wr;

void *private_data;

void (*complete)(void *private_data);

};

3.spi_sync()

spi_sync()函数用于同步传输数据，该函数会等待传输完成并返回传输结果。该函数的代码如下：

int spi_sync(struct spi_device *spi, struct spi_transfer *t)

{

DECLARE_COMPLETION_ONSTACK(done);

int status;

t->complete = spi_complete;

t->private_data = &done;

t->rdy_for_tx = t->rdy_for_rx = 0;

t->cs_change = spi->controller->cs_gpiod ? 1 : 0;

status = spi_async(spi, t);

if (status == 0) {

wait_for_completion(&done);

status = t->status;

if (status == -ETIMEDOUT)

status = -EIO;

}

return status;

}

4.spi_async()

spi_async()函数用于异步传输数据，该函数会启动SPI传输，并立即返回，不等待传输完成。该函数的代码如下：

int spi_async(struct spi_device *spi, struct spi_transfer *t)

{

struct spi_message msg;

int status;

memset(&msg, 0, sizeof(msg));

msg.spi = spi;

msg.complete = spi_complete;

msg.context = t;

msg.state = NULL;

msg.is_dma_mapped = false;

spi_prepare_message(&msg, t);

status = spi_async_locked(spi_get_parent_master(spi), &msg);

if (status == -EBUSY)

return -EAGAIN;

t->status = status;

if (msg.is_dma_mapped)

dma_unmap_sg(&spi->dev, msg.sgbuf, msg.nents, msg.direction);

if (msg.is_dma_mapped && msg.context && spi_need_dma_clean_up_on_error()) {

struct spi_controller *ctlr = spi->controller;

struct spi_transfer *xfer = msg.contexte

if (xfer->tx_buf && ctlr->dma_tx && ctlr->dma_tx->device->dev) {

dma_sync_sg_for_device(ctlr->dma_tx->device->dev,

msg.sgbuf,

msg.nents,

(ctlr->dma_tx_dir == DMA_MEM_TO_DEV) ?

DMA_TO_DEVICE : DMA_FROM_DEVICE);

dma_unmap_sg(ctlr->dma_tx->device->dev,

msg.sgbuf,

msg.nents,

ctlr->dma_tx_dir);

}

if (xfer->rx_buf && ctlr->dma_rx && ctlr->dma_rx->device->dev) {

dma_sync_sg_for_device(ctlr->dma_rx->device->dev,

msg.sgbuf,

msg.nents,

(ctlr->dma_rx_dir == DMA_MEM_TO_DEV) ?

DMA_TO_DEVICE : DMA_FROM_DEVICE);

dma_unmap_sg(ctlr->dma_rx->device->dev,

msg.sgbuf,

msg.nents,

ctlr->dma_rx_dir);

}

}

if (status == -EINPROGRESS || status == -EBUSY) {

status = 0;

} else if (unlikely(status)) {

dev_err(spi->dev.parent, "%s: spi_sync failed with status %d\n",

__func__, status);

}

return status;

}

四、总结

       本文分析了Linux内核中的SPI驱动源码，介绍了SPI驱动框架的基本结构、spi.c的结构和作用以及SPI驱动中的重要数据结构和函数。通读本文后，读者应该了解了SPI设备的工作原理和Linux内核中提供的SPI驱动框架的实现方式，理解了相关代码的运行过程和涉及的系统调用，有助于读者熟练掌握SPI驱动的编写技巧。