基础知识及 SPI 相关结构体介绍
引脚：MISO（master 输入，slave 输出），MOSI（master 输出，slave 输入），片选引脚，SCK（时钟）
控制寄存器：可以设置这CPOL 和 CPHA两个参数，CPOL 代表 SCK 初始电平，CPHA 代表相位（第一/第二个时钟沿采集数据），
SPI 状态寄存器：分辨数据是否发送完了，使能中断
波特率寄存器：设置 SCK 频率
数据寄存器：连接移位器收发数据
驱动程序编写方法：Master 和 slave 都需要驱动程序，采用总线设备驱动模型编写，设备树->spi_dev，驱动程序->spi_driver
/ include / linux / spi / spi.h中定义了 spi_master，里面有 transfer 函数指针
/* Compatibility layer */
#define spi_master spi_controller
struct spi_controller {
struct device dev;
struct list_head list;
/* other than negative (== assign one dynamically), bus_num is fully
* board-specific. usually that simplifies to being SOC-specific.
* example: one SOC has three SPI controllers, numbered 0..2,
* and one board's schematics might show it using SPI-2. software
* would normally use bus_num=2 for that controller.
*/
s16 bus_num;
/* chipselects will be integral to many controllers; some others
* might use board-specific GPIOs.
*/
u16 num_chipselect;
/* some SPI controllers pose alignment requirements on DMAable
* buffers; let protocol drivers know about these requirements.
*/
u16 dma_alignment;
/* spi_device.mode flags understood by this controller driver */
u32 mode_bits;
/* spi_device.mode flags override flags for this controller */
u32 buswidth_override_bits;
/* bitmask of supported bits_per_word for transfers */
u32 bits_per_word_mask;
#define SPI_BPW_MASK(bits) BIT((bits) - 1)
#define SPI_BPW_RANGE_MASK(min, max) GENMASK((max) - 1, (min) - 1)
/* limits on transfer speed */
u32 min_speed_hz;
u32 max_speed_hz;
/* other constraints relevant to this driver */
u16 flags;
#define SPI_CONTROLLER_HALF_DUPLEX BIT(0) /* can't do full duplex */
#define SPI_CONTROLLER_NO_RX BIT(1) /* can't do buffer read */
#define SPI_CONTROLLER_NO_TX BIT(2) /* can't do buffer write */
#define SPI_CONTROLLER_MUST_RX BIT(3) /* requires rx */
#define SPI_CONTROLLER_MUST_TX BIT(4) /* requires tx */
#define SPI_MASTER_GPIO_SS BIT(5) /* GPIO CS must select slave */
/* flag indicating if the allocation of this struct is devres-managed */
bool devm_allocated;
/* flag indicating this is an SPI slave controller */
bool slave;
/*
* on some hardware transfer / message size may be constrained
* the limit may depend on device transfer settings
*/
size_t (*max_transfer_size)(struct spi_device *spi);
size_t (*max_message_size)(struct spi_device *spi);
/* I/O mutex */
struct mutex io_mutex;
/* Used to avoid adding the same CS twice */
struct mutex add_lock;
/* lock and mutex for SPI bus locking */
spinlock_t bus_lock_spinlock;
struct mutex bus_lock_mutex;
/* flag indicating that the SPI bus is locked for exclusive use */
bool bus_lock_flag;
/* Setup mode and clock, etc (spi driver may call many times).
*
* IMPORTANT: this may be called when transfers to another
* device are active. DO NOT UPDATE SHARED REGISTERS in ways
* which could break those transfers.
*/
int (*setup)(struct spi_device *spi);
/*
* set_cs_timing() method is for SPI controllers that supports
* configuring CS timing.
*
* This hook allows SPI client drivers to request SPI controllers
* to configure specific CS timing through spi_set_cs_timing() after
* spi_setup().
*/
int (*set_cs_timing)(struct spi_device *spi);
/* bidirectional bulk transfers
*
* + The transfer() method may not sleep; its main role is
* just to add the message to the queue.
* + For now there's no remove-from-queue operation, or
* any other request management
* + To a given spi_device, message queueing is pure fifo
*
* + The controller's main job is to process its message queue,
* selecting a chip (for masters), then transferring data
* + If there are multiple spi_device children, the i/o queue
* arbitration algorithm is unspecified (round robin, fifo,
* priority, reservations, preemption, etc)
*
* + Chipselect stays active during the entire message
* (unless modified by spi_transfer.cs_change != 0).
* + The message transfers use clock and SPI mode parameters
* previously established by setup() for this device
*/
int (*transfer)(struct spi_device *spi,
struct spi_message *mesg);
/* called on release() to free memory provided by spi_controller */
void (*cleanup)(struct spi_device *spi);
/*
* Used to enable core support for DMA handling, if can_dma()
* exists and returns true then the transfer will be mapped
* prior to transfer_one() being called. The driver should
* not modify or store xfer and dma_tx and dma_rx must be set
* while the device is prepared.
*/
bool (*can_dma)(struct spi_controller *ctlr,
struct spi_device *spi,
struct spi_transfer *xfer);
struct device *dma_map_dev;
/*
* These hooks are for drivers that want to use the generic
* controller transfer queueing mechanism. If these are used, the
* transfer() function above must NOT be specified by the driver.
* Over time we expect SPI drivers to be phased over to this API.
*/
bool queued;
struct kthread_worker *kworker;
struct kthread_work pump_messages;
spinlock_t queue_lock;
struct list_head queue;
struct spi_message *cur_msg;
bool idling;
bool busy;
bool running;
bool rt;
bool auto_runtime_pm;
bool cur_msg_prepared;
bool cur_msg_mapped;
char last_cs;
bool last_cs_mode_high;
bool fallback;
struct completion xfer_completion;
size_t max_dma_len;
int (*prepare_transfer_hardware)(struct spi_controller *ctlr);
int (*transfer_one_message)(struct spi_controller *ctlr,
struct spi_message *mesg);
int (*unprepare_transfer_hardware)(struct spi_controller *ctlr);
int (*prepare_message)(struct spi_controller *ctlr,
struct spi_message *message);
int (*unprepare_message)(struct spi_controller *ctlr,
struct spi_message *message);
int (*slave_abort)(struct spi_controller *ctlr);
/*
* These hooks are for drivers that use a generic implementation
* of transfer_one_message() provided by the core.
*/
void (*set_cs)(struct spi_device *spi, bool enable);
int (*transfer_one)(struct spi_controller *ctlr, struct spi_device *spi,
struct spi_transfer *transfer);
void (*handle_err)(struct spi_controller *ctlr,
struct spi_message *message);
/* Optimized handlers for SPI memory-like operations. */
const struct spi_controller_mem_ops *mem_ops;
const struct spi_controller_mem_caps *mem_caps;
/* gpio chip select */
struct gpio_desc **cs_gpiods;
bool use_gpio_descriptors;
s8 unused_native_cs;
s8 max_native_cs;
/* statistics */
struct spi_statistics statistics;
/* DMA channels for use with core dmaengine helpers */
struct dma_chan *dma_tx;
struct dma_chan *dma_rx;
/* dummy data for full duplex devices */
void *dummy_rx;
void *dummy_tx;
int (*fw_translate_cs)(struct spi_controller *ctlr, unsigned cs);
/*
* Driver sets this field to indicate it is able to snapshot SPI
* transfers (needed e.g. for reading the time of POSIX clocks)
*/
bool ptp_sts_supported;
/* Interrupt enable state during PTP system timestamping */
unsigned long irq_flags;
};spi_device 结构体，可以看到这里结构体里面包含spi_controller，由设备树转换得到，其中bits_per_word 是每次传输的位数
struct spi_device {
struct device dev;
struct spi_controller *controller;
struct spi_controller *master; /* compatibility layer */
u32 max_speed_hz;
u8 chip_select;
u8 bits_per_word;
bool rt;
#define SPI_NO_TX BIT(31) /* no transmit wire */
#define SPI_NO_RX BIT(30) /* no receive wire */
/*
* All bits defined above should be covered by SPI_MODE_KERNEL_MASK.
* The SPI_MODE_KERNEL_MASK has the SPI_MODE_USER_MASK counterpart,
* which is defined in 'include/uapi/linux/spi/spi.h'.
* The bits defined here are from bit 31 downwards, while in
* SPI_MODE_USER_MASK are from 0 upwards.
* These bits must not overlap. A static assert check should make sure of that.
* If adding extra bits, make sure to decrease the bit index below as well.
*/
#define SPI_MODE_KERNEL_MASK (~(BIT(30) - 1))
u32 mode;
int irq;
void *controller_state;
void *controller_data;
char modalias[SPI_NAME_SIZE];
const char *driver_override;
struct gpio_desc *cs_gpiod; /* chip select gpio desc */
struct spi_delay word_delay; /* inter-word delay */
/* CS delays */
struct spi_delay cs_setup;
struct spi_delay cs_hold;
struct spi_delay cs_inactive;
/* the statistics */
struct spi_statistics statistics;
/*
* likely need more hooks for more protocol options affecting how
* the controller talks to each chip, like:
* - memory packing (12 bit samples into low bits, others zeroed)
* - priority
* - chipselect delays
* - ...
*/
};spi_driver 结构体
struct spi_driver {
const struct spi_device_id *id_table;
int (*probe)(struct spi_device *spi);
void (*remove)(struct spi_device *spi);
void (*shutdown)(struct spi_device *spi);
struct device_driver driver;
};设备树结构：
spi{
spi master 配置（address-cell，size-cell，reg，interrupts，interrupt-parent，cs-gpios，compatible，spi-cpol，spi-cpha......）
slave{spi_device}
slave{spi_device}
}
设备树处理过程
首先根据spi 的compatible 属性找到 master 驱动，然后由 master 驱动解析子节点
看看内核的处理过程，设备树匹配之后 调用 probe 函数
/ drivers / spi / spi-gpio.c
static struct platform_driver spi_gpio_driver = {
.driver = {
.name = DRIVER_NAME,
.of_match_table = of_match_ptr(spi_gpio_dt_ids),
},
.probe = spi_gpio_probe,
};
module_platform_driver(spi_gpio_driver);首先设置 master 的参数
static int spi_gpio_probe(struct platform_device *pdev)
{
int status;
struct spi_master *master;
struct spi_gpio *spi_gpio;
struct device *dev = &pdev->dev;
struct spi_bitbang *bb;
master = devm_spi_alloc_master(dev, sizeof(*spi_gpio));
if (!master)
return -ENOMEM;
if (pdev->dev.of_node)
status = spi_gpio_probe_dt(pdev, master);
else
status = spi_gpio_probe_pdata(pdev, master);
if (status)
return status;
spi_gpio = spi_master_get_devdata(master);
status = spi_gpio_request(dev, spi_gpio);
if (status)
return status;
master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
SPI_CS_HIGH | SPI_LSB_FIRST;
if (!spi_gpio->mosi) {
/* HW configuration without MOSI pin
*
* No setting SPI_MASTER_NO_RX here - if there is only
* a MOSI pin connected the host can still do RX by
* changing the direction of the line.
*/
master->flags = SPI_MASTER_NO_TX;
}
master->bus_num = pdev->id;
master->setup = spi_gpio_setup;
master->cleanup = spi_gpio_cleanup;
bb = &spi_gpio->bitbang;
bb->master = master;
/*
* There is some additional business, apart from driving the CS GPIO
* line, that we need to do on selection. This makes the local
* callback for chipselect always get called.
*/
master->flags |= SPI_MASTER_GPIO_SS;
bb->chipselect = spi_gpio_chipselect;
bb->set_line_direction = spi_gpio_set_direction;
if (master->flags & SPI_MASTER_NO_TX) {
bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
} else {
bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
}
bb->setup_transfer = spi_bitbang_setup_transfer;
status = spi_bitbang_init(&spi_gpio->bitbang);
if (status)
return status;
return devm_spi_register_master(&pdev->dev, master);
}
/ include / linux / spi / spi.h
#define devm_spi_register_master(_dev, _ctlr) \
devm_spi_register_controller(_dev, _ctlr)/ drivers / spi / spi.c
/**
* devm_spi_register_controller - register managed SPI master or slave
* controller
* @dev: device managing SPI controller
* @ctlr: initialized controller, originally from spi_alloc_master() or
* spi_alloc_slave()
* Context: can sleep
*
* Register a SPI device as with spi_register_controller() which will
* automatically be unregistered and freed.
*
* Return: zero on success, else a negative error code.
*/
int devm_spi_register_controller(struct device *dev,
struct spi_controller *ctlr)
{
struct spi_controller **ptr;
int ret;
ptr = devres_alloc(devm_spi_unregister, sizeof(*ptr), GFP_KERNEL);
if (!ptr)
return -ENOMEM;
ret = spi_register_controller(ctlr);
if (!ret) {
*ptr = ctlr;
devres_add(dev, ptr);
} else {
devres_free(ptr);
}
return ret;
}
EXPORT_SYMBOL_GPL(devm_spi_register_controller);注册 master
int spi_register_controller(struct spi_controller *ctlr)
{
struct device *dev = ctlr->dev.parent;
struct boardinfo *bi;
int status;
int id, first_dynamic;
if (!dev)
return -ENODEV;
/*
* Make sure all necessary hooks are implemented before registering
* the SPI controller.
*/
status = spi_controller_check_ops(ctlr);
if (status)
return status;
if (ctlr->bus_num >= 0) {
/* devices with a fixed bus num must check-in with the num */
mutex_lock(&board_lock);
id = idr_alloc(&spi_master_idr, ctlr, ctlr->bus_num,
ctlr->bus_num + 1, GFP_KERNEL);
mutex_unlock(&board_lock);
if (WARN(id < 0, "couldn't get idr"))
return id == -ENOSPC ? -EBUSY : id;
ctlr->bus_num = id;
} else if (ctlr->dev.of_node) {
/* allocate dynamic bus number using Linux idr */
id = of_alias_get_id(ctlr->dev.of_node, "spi");
if (id >= 0) {
ctlr->bus_num = id;
mutex_lock(&board_lock);
id = idr_alloc(&spi_master_idr, ctlr, ctlr->bus_num,
ctlr->bus_num + 1, GFP_KERNEL);
mutex_unlock(&board_lock);
if (WARN(id < 0, "couldn't get idr"))
return id == -ENOSPC ? -EBUSY : id;
}
}
if (ctlr->bus_num < 0) {
first_dynamic = of_alias_get_highest_id("spi");
if (first_dynamic < 0)
first_dynamic = 0;
else
first_dynamic++;
mutex_lock(&board_lock);
id = idr_alloc(&spi_master_idr, ctlr, first_dynamic,
0, GFP_KERNEL);
mutex_unlock(&board_lock);
if (WARN(id < 0, "couldn't get idr"))
return id;
ctlr->bus_num = id;
}
ctlr->bus_lock_flag = 0;
init_completion(&ctlr->xfer_completion);
if (!ctlr->max_dma_len)
ctlr->max_dma_len = INT_MAX;
/*
* Register the device, then userspace will see it.
* Registration fails if the bus ID is in use.
*/
dev_set_name(&ctlr->dev, "spi%u", ctlr->bus_num);
if (!spi_controller_is_slave(ctlr) && ctlr->use_gpio_descriptors) {
status = spi_get_gpio_descs(ctlr);
if (status)
goto free_bus_id;
/*
* A controller using GPIO descriptors always
* supports SPI_CS_HIGH if need be.
*/
ctlr->mode_bits |= SPI_CS_HIGH;
}
/*
* Even if it's just one always-selected device, there must
* be at least one chipselect.
*/
if (!ctlr->num_chipselect) {
status = -EINVAL;
goto free_bus_id;
}
/* setting last_cs to -1 means no chip selected */
ctlr->last_cs = -1;
status = device_add(&ctlr->dev);
if (status < 0)
goto free_bus_id;
dev_dbg(dev, "registered %s %s\n",
spi_controller_is_slave(ctlr) ? "slave" : "master",
dev_name(&ctlr->dev));
/*
* If we're using a queued driver, start the queue. Note that we don't
* need the queueing logic if the driver is only supporting high-level
* memory operations.
*/
if (ctlr->transfer) {
dev_info(dev, "controller is unqueued, this is deprecated\n");
} else if (ctlr->transfer_one || ctlr->transfer_one_message) {
status = spi_controller_initialize_queue(ctlr);
if (status) {
device_del(&ctlr->dev);
goto free_bus_id;
}
}
/* add statistics */
spin_lock_init(&ctlr->statistics.lock);
mutex_lock(&board_lock);
list_add_tail(&ctlr->list, &spi_controller_list);
list_for_each_entry(bi, &board_list, list)
spi_match_controller_to_boardinfo(ctlr, &bi->board_info);
mutex_unlock(&board_lock);
/* Register devices from the device tree and ACPI */
of_register_spi_devices(ctlr);
acpi_register_spi_devices(ctlr);
return status;
free_bus_id:
mutex_lock(&board_lock);
idr_remove(&spi_master_idr, ctlr->bus_num);
mutex_unlock(&board_lock);
return status;
}
EXPORT_SYMBOL_GPL(spi_register_controller);可以看到这里遍历子节点然后区进行注册
static void of_register_spi_devices(struct spi_controller *ctlr)
{
struct spi_device *spi;
struct device_node *nc;
if (!ctlr->dev.of_node)
return;
for_each_available_child_of_node(ctlr->dev.of_node, nc) {
if (of_node_test_and_set_flag(nc, OF_POPULATED))
continue;
spi = of_register_spi_device(ctlr, nc);
if (IS_ERR(spi)) {
dev_warn(&ctlr->dev,
"Failed to create SPI device for %pOF\n", nc);
of_node_clear_flag(nc, OF_POPULATED);
}
}
}static struct spi_device *
of_register_spi_device(struct spi_controller *ctlr, struct device_node *nc)
{
struct spi_device *spi;
int rc;
/* Alloc an spi_device */
spi = spi_alloc_device(ctlr);
if (!spi) {
dev_err(&ctlr->dev, "spi_device alloc error for %pOF\n", nc);
rc = -ENOMEM;
goto err_out;
}
/* Select device driver */
rc = of_modalias_node(nc, spi->modalias,
sizeof(spi->modalias));
if (rc < 0) {
dev_err(&ctlr->dev, "cannot find modalias for %pOF\n", nc);
goto err_out;
}
rc = of_spi_parse_dt(ctlr, spi, nc);
if (rc)
goto err_out;
/* Store a pointer to the node in the device structure */
of_node_get(nc);
spi->dev.of_node = nc;
spi->dev.fwnode = of_fwnode_handle(nc);
/* Register the new device */
rc = spi_add_device(spi);
if (rc) {
dev_err(&ctlr->dev, "spi_device register error %pOF\n", nc);
goto err_of_node_put;
}
return spi;
err_of_node_put:
of_node_put(nc);
err_out:
spi_dev_put(spi);
return ERR_PTR(rc);
}spidev 驱动源码解析
insmod 之后会调用 init 函数
/ drivers / spi / spidev.c
这里面注册了一个字符设备驱动和 spi_driver
static int __init spidev_init(void)
{
int status;
/* Claim our 256 reserved device numbers. Then register a class
* that will key udev/mdev to add/remove /dev nodes. Last, register
* the driver which manages those device numbers.
*/
status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);
if (status < 0)
return status;
spidev_class = class_create(THIS_MODULE, "spidev");
if (IS_ERR(spidev_class)) {
unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
return PTR_ERR(spidev_class);
}
status = spi_register_driver(&spidev_spi_driver);
if (status < 0) {
class_destroy(spidev_class);
unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
}
return status;
}
module_init(spidev_init);设备树匹配之后 probe 函数被调用
static struct spi_driver spidev_spi_driver = {
.driver = {
.name = "spidev",
.of_match_table = spidev_dt_ids,
.acpi_match_table = spidev_acpi_ids,
},
.probe = spidev_probe,
.remove = spidev_remove,
.id_table = spidev_spi_ids,
/* NOTE: suspend/resume methods are not necessary here.
* We don't do anything except pass the requests to/from
* the underlying controller. The refrigerator handles
* most issues; the controller driver handles the rest.
*/
};来看看 probe 函数，这里首先记录 spi 设备，然后找到一个次设备号并创建设备节点，创建之后可以在/dev/找到这个字符设备，用户访问时通过下面的device_list 找出spidev_data（有spi_device），spi_device 中又包含了 spi_master，这样就可以通过spi_master 读写设备了
static int spidev_probe(struct spi_device *spi)
{
int (*match)(struct device *dev);
struct spidev_data *spidev;
int status;
unsigned long minor;
match = device_get_match_data(&spi->dev);
if (match) {
status = match(&spi->dev);
if (status)
return status;
}
/* Allocate driver data */
spidev = kzalloc(sizeof(*spidev), GFP_KERNEL);
if (!spidev)
return -ENOMEM;
/* Initialize the driver data */
spidev->spi = spi;
spin_lock_init(&spidev->spi_lock);
mutex_init(&spidev->buf_lock);
INIT_LIST_HEAD(&spidev->device_entry);
/* If we can allocate a minor number, hook up this device.
* Reusing minors is fine so long as udev or mdev is working.
*/
mutex_lock(&device_list_lock);
minor = find_first_zero_bit(minors, N_SPI_MINORS);
if (minor < N_SPI_MINORS) {
struct device *dev;
spidev->devt = MKDEV(SPIDEV_MAJOR, minor);
dev = device_create(spidev_class, &spi->dev, spidev->devt,
spidev, "spidev%d.%d",
spi->master->bus_num, spi->chip_select);
status = PTR_ERR_OR_ZERO(dev);
} else {
dev_dbg(&spi->dev, "no minor number available!\n");
status = -ENODEV;
}
if (status == 0) {
set_bit(minor, minors);
list_add(&spidev->device_entry, &device_list);
}
mutex_unlock(&device_list_lock);
spidev->speed_hz = spi->max_speed_hz;
if (status == 0)
spi_set_drvdata(spi, spidev);
else
kfree(spidev);
return status;
}用户就使用这里字符设备驱动程序提供的接口去操作 spidev 了，其中 spi 读写操作的实现都在其中
static const struct file_operations spidev_fops = {
.owner = THIS_MODULE,
/* REVISIT switch to aio primitives, so that userspace
* gets more complete API coverage. It'll simplify things
* too, except for the locking.
*/
.write = spidev_write,
.read = spidev_read,
.unlocked_ioctl = spidev_ioctl,
.compat_ioctl = spidev_compat_ioctl,
.open = spidev_open,
.release = spidev_release,
.llseek = no_llseek,
};内核应用程序参考代码
/ tools / spi / spidev_fdx.c
// SPDX-License-Identifier: GPL-2.0
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <linux/types.h>
#include <linux/spi/spidev.h>
static int verbose;
static void do_read(int fd, int len)
{
unsigned char buf[32], *bp;
int status;
/* read at least 2 bytes, no more than 32 */
if (len < 2)
len = 2;
else if (len > sizeof(buf))
len = sizeof(buf);
memset(buf, 0, sizeof buf);
status = read(fd, buf, len);
if (status < 0) {
perror("read");
return;
}
if (status != len) {
fprintf(stderr, "short read\n");
return;
}
printf("read(%2d, %2d): %02x %02x,", len, status,
buf[0], buf[1]);
status -= 2;
bp = buf + 2;
while (status-- > 0)
printf(" %02x", *bp++);
printf("\n");
}
static void do_msg(int fd, int len)
{
struct spi_ioc_transfer xfer[2];
unsigned char buf[32], *bp;
int status;
memset(xfer, 0, sizeof xfer);
memset(buf, 0, sizeof buf);
if (len > sizeof buf)
len = sizeof buf;
buf[0] = 0xaa;
xfer[0].tx_buf = (unsigned long)buf;
xfer[0].len = 1;
xfer[1].rx_buf = (unsigned long) buf;
xfer[1].len = len;
status = ioctl(fd, SPI_IOC_MESSAGE(2), xfer);
if (status < 0) {
perror("SPI_IOC_MESSAGE");
return;
}
printf("response(%2d, %2d): ", len, status);
for (bp = buf; len; len--)
printf(" %02x", *bp++);
printf("\n");
}
static void dumpstat(const char *name, int fd)
{
__u8 lsb, bits;
__u32 mode, speed;
if (ioctl(fd, SPI_IOC_RD_MODE32, &mode) < 0) {
perror("SPI rd_mode");
return;
}
if (ioctl(fd, SPI_IOC_RD_LSB_FIRST, &lsb) < 0) {
perror("SPI rd_lsb_fist");
return;
}
if (ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits) < 0) {
perror("SPI bits_per_word");
return;
}
if (ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed) < 0) {
perror("SPI max_speed_hz");
return;
}
printf("%s: spi mode 0x%x, %d bits %sper word, %d Hz max\n",
name, mode, bits, lsb ? "(lsb first) " : "", speed);
}
int main(int argc, char **argv)
{
int c;
int readcount = 0;
int msglen = 0;
int fd;
const char *name;
while ((c = getopt(argc, argv, "hm:r:v")) != EOF) {
switch (c) {
case 'm':
msglen = atoi(optarg);
if (msglen < 0)
goto usage;
continue;
case 'r':
readcount = atoi(optarg);
if (readcount < 0)
goto usage;
continue;
case 'v':
verbose++;
continue;
case 'h':
case '?':
usage:
fprintf(stderr,
"usage: %s [-h] [-m N] [-r N] /dev/spidevB.D\n",
argv[0]);
return 1;
}
}
if ((optind + 1) != argc)
goto usage;
name = argv[optind];
fd = open(name, O_RDWR);
if (fd < 0) {
perror("open");
return 1;
}
dumpstat(name, fd);
if (msglen)
do_msg(fd, msglen);
if (readcount)
do_read(fd, readcount);
close(fd);
return 0;
}spi 发送源码解析
/ drivers / spi / spidev.c
/* Write-only message with current device setup */
static ssize_t
spidev_write(struct file *filp, const char __user *buf,
size_t count, loff_t *f_pos)
{
struct spidev_data *spidev;
ssize_t status;
unsigned long missing;
/* chipselect only toggles at start or end of operation */
if (count > bufsiz)
return -EMSGSIZE;
spidev = filp->private_data;
mutex_lock(&spidev->buf_lock);
missing = copy_from_user(spidev->tx_buffer, buf, count);
if (missing == 0)
status = spidev_sync_write(spidev, count);
else
status = -EFAULT;
mutex_unlock(&spidev->buf_lock);
return status;
}static inline ssize_t
spidev_sync_write(struct spidev_data *spidev, size_t len)
{
struct spi_transfer t = {
.tx_buf = spidev->tx_buffer,
.len = len,
.speed_hz = spidev->speed_hz,
};
struct spi_message m;
spi_message_init(&m);
spi_message_add_tail(&t, &m);
return spidev_sync(spidev, &m);
}static ssize_t
spidev_sync(struct spidev_data *spidev, struct spi_message *message)
{
int status;
struct spi_device *spi;
spin_lock_irq(&spidev->spi_lock);
spi = spidev->spi;
spin_unlock_irq(&spidev->spi_lock);
if (spi == NULL)
status = -ESHUTDOWN;
else
status = spi_sync(spi, message);
if (status == 0)
status = message->actual_length;
return status;
}/ drivers / spi / spi.c
/**
* spi_sync - blocking/synchronous SPI data transfers
* @spi: device with which data will be exchanged
* @message: describes the data transfers
* Context: can sleep
*
* This call may only be used from a context that may sleep. The sleep
* is non-interruptible, and has no timeout. Low-overhead controller
* drivers may DMA directly into and out of the message buffers.
*
* Note that the SPI device's chip select is active during the message,
* and then is normally disabled between messages. Drivers for some
* frequently-used devices may want to minimize costs of selecting a chip,
* by leaving it selected in anticipation that the next message will go
* to the same chip. (That may increase power usage.)
*
* Also, the caller is guaranteeing that the memory associated with the
* message will not be freed before this call returns.
*
* Return: zero on success, else a negative error code.
*/
int spi_sync(struct spi_device *spi, struct spi_message *message)
{
int ret;
mutex_lock(&spi->controller->bus_lock_mutex);
ret = __spi_sync(spi, message);
mutex_unlock(&spi->controller->bus_lock_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(spi_sync);注意这里有 __spi_queued_transfer （把消息放入队列，帮你管理，后面调用__spi_pump_messages 发送消息）和spi_async_locked（自己实现 transfer，自己管理） 两种传输方式
static int __spi_sync(struct spi_device *spi, struct spi_message *message)
{
DECLARE_COMPLETION_ONSTACK(done);
int status;
struct spi_controller *ctlr = spi->controller;
unsigned long flags;
status = __spi_validate(spi, message);
if (status != 0)
return status;
message->complete = spi_complete;
message->context = &done;
message->spi = spi;
SPI_STATISTICS_INCREMENT_FIELD(&ctlr->statistics, spi_sync);
SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics, spi_sync);
/*
* If we're not using the legacy transfer method then we will
* try to transfer in the calling context so special case.
* This code would be less tricky if we could remove the
* support for driver implemented message queues.
*/
if (ctlr->transfer == spi_queued_transfer) {
spin_lock_irqsave(&ctlr->bus_lock_spinlock, flags);
trace_spi_message_submit(message);
status = __spi_queued_transfer(spi, message, false);
spin_unlock_irqrestore(&ctlr->bus_lock_spinlock, flags);
} else {
status = spi_async_locked(spi, message);
}
if (status == 0) {
/* Push out the messages in the calling context if we can */
if (ctlr->transfer == spi_queued_transfer) {
SPI_STATISTICS_INCREMENT_FIELD(&ctlr->statistics,
spi_sync_immediate);
SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics,
spi_sync_immediate);
__spi_pump_messages(ctlr, false);
}
wait_for_completion(&done);
status = message->status;
}
message->context = NULL;
return status;
}先看 spi_async_locked
static int spi_async_locked(struct spi_device *spi, struct spi_message *message)
{
struct spi_controller *ctlr = spi->controller;
int ret;
unsigned long flags;
ret = __spi_validate(spi, message);
if (ret != 0)
return ret;
spin_lock_irqsave(&ctlr->bus_lock_spinlock, flags);
ret = __spi_async(spi, message);
spin_unlock_irqrestore(&ctlr->bus_lock_spinlock, flags);
return ret;
在这里可以看到需要自己提供 transfer 函数，需要自己管理队列，自己触发传输
static int __spi_async(struct spi_device *spi, struct spi_message *message)
{
struct spi_controller *ctlr = spi->controller;
struct spi_transfer *xfer;
/*
* Some controllers do not support doing regular SPI transfers. Return
* ENOTSUPP when this is the case.
*/
if (!ctlr->transfer)
return -ENOTSUPP;
message->spi = spi;
SPI_STATISTICS_INCREMENT_FIELD(&ctlr->statistics, spi_async);
SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics, spi_async);
trace_spi_message_submit(message);
if (!ctlr->ptp_sts_supported) {
list_for_each_entry(xfer, &message->transfers, transfer_list) {
xfer->ptp_sts_word_pre = 0;
ptp_read_system_prets(xfer->ptp_sts);
}
}
return ctlr->transfer(spi, message);
}来看看__spi_queued_transfer，如果 transfer 函数是内核提供的话就会调用这个函数
static int __spi_queued_transfer(struct spi_device *spi,
struct spi_message *msg,
bool need_pump)
{
struct spi_controller *ctlr = spi->controller;
unsigned long flags;
spin_lock_irqsave(&ctlr->queue_lock, flags);
if (!ctlr->running) {
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
return -ESHUTDOWN;
}
msg->actual_length = 0;
msg->status = -EINPROGRESS;
list_add_tail(&msg->queue, &ctlr->queue);
if (!ctlr->busy && need_pump)
kthread_queue_work(ctlr->kworker, &ctlr->pump_messages);
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
return 0;
}来看看前面的__spi_pump_messages，这里调用transfer_one_message传输一个消息，就是循环发送消息中的所有 xfer
/**
* __spi_pump_messages - function which processes spi message queue
* @ctlr: controller to process queue for
* @in_kthread: true if we are in the context of the message pump thread
*
* This function checks if there is any spi message in the queue that
* needs processing and if so call out to the driver to initialize hardware
* and transfer each message.
*
* Note that it is called both from the kthread itself and also from
* inside spi_sync(); the queue extraction handling at the top of the
* function should deal with this safely.
*/
static void __spi_pump_messages(struct spi_controller *ctlr, bool in_kthread)
{
struct spi_transfer *xfer;
struct spi_message *msg;
bool was_busy = false;
unsigned long flags;
int ret;
/* Lock queue */
spin_lock_irqsave(&ctlr->queue_lock, flags);
/* Make sure we are not already running a message */
if (ctlr->cur_msg) {
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
return;
}
/* If another context is idling the device then defer */
if (ctlr->idling) {
kthread_queue_work(ctlr->kworker, &ctlr->pump_messages);
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
return;
}
/* Check if the queue is idle */
if (list_empty(&ctlr->queue) || !ctlr->running) {
if (!ctlr->busy) {
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
return;
}
/* Defer any non-atomic teardown to the thread */
if (!in_kthread) {
if (!ctlr->dummy_rx && !ctlr->dummy_tx &&
!ctlr->unprepare_transfer_hardware) {
spi_idle_runtime_pm(ctlr);
ctlr->busy = false;
trace_spi_controller_idle(ctlr);
} else {
kthread_queue_work(ctlr->kworker,
&ctlr->pump_messages);
}
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
return;
}
ctlr->busy = false;
ctlr->idling = true;
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
kfree(ctlr->dummy_rx);
ctlr->dummy_rx = NULL;
kfree(ctlr->dummy_tx);
ctlr->dummy_tx = NULL;
if (ctlr->unprepare_transfer_hardware &&
ctlr->unprepare_transfer_hardware(ctlr))
dev_err(&ctlr->dev,
"failed to unprepare transfer hardware\n");
spi_idle_runtime_pm(ctlr);
trace_spi_controller_idle(ctlr);
spin_lock_irqsave(&ctlr->queue_lock, flags);
ctlr->idling = false;
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
return;
}
/* Extract head of queue */
msg = list_first_entry(&ctlr->queue, struct spi_message, queue);
ctlr->cur_msg = msg;
list_del_init(&msg->queue);
if (ctlr->busy)
was_busy = true;
else
ctlr->busy = true;
spin_unlock_irqrestore(&ctlr->queue_lock, flags);
mutex_lock(&ctlr->io_mutex);
if (!was_busy && ctlr->auto_runtime_pm) {
ret = pm_runtime_resume_and_get(ctlr->dev.parent);
if (ret < 0) {
dev_err(&ctlr->dev, "Failed to power device: %d\n",
ret);
mutex_unlock(&ctlr->io_mutex);
return;
}
}
if (!was_busy)
trace_spi_controller_busy(ctlr);
if (!was_busy && ctlr->prepare_transfer_hardware) {
ret = ctlr->prepare_transfer_hardware(ctlr);
if (ret) {
dev_err(&ctlr->dev,
"failed to prepare transfer hardware: %d\n",
ret);
if (ctlr->auto_runtime_pm)
pm_runtime_put(ctlr->dev.parent);
msg->status = ret;
spi_finalize_current_message(ctlr);
mutex_unlock(&ctlr->io_mutex);
return;
}
}
trace_spi_message_start(msg);
if (ctlr->prepare_message) {
ret = ctlr->prepare_message(ctlr, msg);
if (ret) {
dev_err(&ctlr->dev, "failed to prepare message: %d\n",
ret);
msg->status = ret;
spi_finalize_current_message(ctlr);
goto out;
}
ctlr->cur_msg_prepared = true;
}
ret = spi_map_msg(ctlr, msg);
if (ret) {
msg->status = ret;
spi_finalize_current_message(ctlr);
goto out;
}
if (!ctlr->ptp_sts_supported && !ctlr->transfer_one) {
list_for_each_entry(xfer, &msg->transfers, transfer_list) {
xfer->ptp_sts_word_pre = 0;
ptp_read_system_prets(xfer->ptp_sts);
}
}
ret = ctlr->transfer_one_message(ctlr, msg);
if (ret) {
dev_err(&ctlr->dev,
"failed to transfer one message from queue: %d\n",
ret);
goto out;
}
out:
mutex_unlock(&ctlr->io_mutex);
/* Prod the scheduler in case transfer_one() was busy waiting */
if (!ret)
cond_resched();
}spi master 驱动分析
/ drivers / spi / spi-gpio.c
首先看 probe 函数，这里先分配一个 spi_master 结构体
static int spi_gpio_probe(struct platform_device *pdev)
{
int status;
struct spi_master *master;
struct spi_gpio *spi_gpio;
struct device *dev = &pdev->dev;
struct spi_bitbang *bb;
master = devm_spi_alloc_master(dev, sizeof(*spi_gpio));
if (!master)
return -ENOMEM;
if (pdev->dev.of_node)
status = spi_gpio_probe_dt(pdev, master);
else
status = spi_gpio_probe_pdata(pdev, master);
if (status)
return status;
spi_gpio = spi_master_get_devdata(master);
status = spi_gpio_request(dev, spi_gpio);
if (status)
return status;
master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
SPI_CS_HIGH | SPI_LSB_FIRST;
if (!spi_gpio->mosi) {
/* HW configuration without MOSI pin
*
* No setting SPI_MASTER_NO_RX here - if there is only
* a MOSI pin connected the host can still do RX by
* changing the direction of the line.
*/
master->flags = SPI_MASTER_NO_TX;
}
master->bus_num = pdev->id;
master->setup = spi_gpio_setup;
master->cleanup = spi_gpio_cleanup;
bb = &spi_gpio->bitbang;
bb->master = master;
/*
* There is some additional business, apart from driving the CS GPIO
* line, that we need to do on selection. This makes the local
* callback for chipselect always get called.
*/
master->flags |= SPI_MASTER_GPIO_SS;
bb->chipselect = spi_gpio_chipselect;
bb->set_line_direction = spi_gpio_set_direction;
if (master->flags & SPI_MASTER_NO_TX) {
bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
} else {
bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
}
bb->setup_transfer = spi_bitbang_setup_transfer;
status = spi_bitbang_init(&spi_gpio->bitbang);
if (status)
return status;
return devm_spi_register_master(&pdev->dev, master);
}这里最核心的就是 bitbang对于 消息收发处理的设置
来看看 bitbang 怎么获取的
/ include / linux / spi / spi.h
#define spi_master_get_devdata(_ctlr) spi_controller_get_devdata(_ctlr)static inline void *spi_controller_get_devdata(struct spi_controller *ctlr)
{
return dev_get_drvdata(&ctlr->dev);
}/ include / linux / device.h
static inline void *dev_get_drvdata(const struct device *dev)
{
return dev->driver_data;
}来看看 bitbang 的具体处理
/ drivers / spi / spi-gpio.c
/ drivers / spi / spi-bitbang.c
可以看到这里对txrx_bufs 进行了赋值，对transfer_one 也进行了赋值
int spi_bitbang_init(struct spi_bitbang *bitbang)
{
struct spi_master *master = bitbang->master;
bool custom_cs;
if (!master)
return -EINVAL;
/*
* We only need the chipselect callback if we are actually using it.
* If we just use GPIO descriptors, it is surplus. If the
* SPI_MASTER_GPIO_SS flag is set, we always need to call the
* driver-specific chipselect routine.
*/
custom_cs = (!master->use_gpio_descriptors ||
(master->flags & SPI_MASTER_GPIO_SS));
if (custom_cs && !bitbang->chipselect)
return -EINVAL;
mutex_init(&bitbang->lock);
if (!master->mode_bits)
master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
if (master->transfer || master->transfer_one_message)
return -EINVAL;
master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
master->transfer_one = spi_bitbang_transfer_one;
/*
* When using GPIO descriptors, the ->set_cs() callback doesn't even
* get called unless SPI_MASTER_GPIO_SS is set.
*/
if (custom_cs)
master->set_cs = spi_bitbang_set_cs;
if (!bitbang->txrx_bufs) {
bitbang->use_dma = 0;
bitbang->txrx_bufs = spi_bitbang_bufs;
if (!master->setup) {
if (!bitbang->setup_transfer)
bitbang->setup_transfer =
spi_bitbang_setup_transfer;
master->setup = spi_bitbang_setup;
master->cleanup = spi_bitbang_cleanup;
}
}
return 0;
}
EXPORT_SYMBOL_GPL(spi_bitbang_init);这里就是正真硬件相关读写了
static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
{
struct spi_bitbang_cs *cs = spi->controller_state;
unsigned nsecs = cs->nsecs;
struct spi_bitbang *bitbang;
bitbang = spi_master_get_devdata(spi->master);
if (bitbang->set_line_direction) {
int err;
err = bitbang->set_line_direction(spi, !!(t->tx_buf));
if (err < 0)
return err;
}
if (spi->mode & SPI_3WIRE) {
unsigned flags;
flags = t->tx_buf ? SPI_MASTER_NO_RX : SPI_MASTER_NO_TX;
return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags);
}
return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0);
}来看看spi_bitbang_transfer_one，可以看到这里面调用了txrx_bufs
static int spi_bitbang_transfer_one(struct spi_master *master,
struct spi_device *spi,
struct spi_transfer *transfer)
{
struct spi_bitbang *bitbang = spi_master_get_devdata(master);
int status = 0;
if (bitbang->setup_transfer) {
status = bitbang->setup_transfer(spi, transfer);
if (status < 0)
goto out;
}
if (transfer->len)
status = bitbang->txrx_bufs(spi, transfer);
if (status == transfer->len)
status = 0;
else if (status >= 0)
status = -EREMOTEIO;
out:
spi_finalize_current_transfer(master);
return status;
}前面提到的transfer_one_message 是在 controller 队列初始化时赋值的
/ drivers / spi / spi.c
static int spi_controller_initialize_queue(struct spi_controller *ctlr)
{
int ret;
ctlr->transfer = spi_queued_transfer;
if (!ctlr->transfer_one_message)
ctlr->transfer_one_message = spi_transfer_one_message;
/* Initialize and start queue */
ret = spi_init_queue(ctlr);
if (ret) {
dev_err(&ctlr->dev, "problem initializing queue\n");
goto err_init_queue;
}
ctlr->queued = true;
ret = spi_start_queue(ctlr);
if (ret) {
dev_err(&ctlr->dev, "problem starting queue\n");
goto err_start_queue;
}
return 0;
err_start_queue:
spi_destroy_queue(ctlr);
err_init_queue:
return ret;
}可以看到这里调用了transfer_one
/*
* spi_transfer_one_message - Default implementation of transfer_one_message()
*
* This is a standard implementation of transfer_one_message() for
* drivers which implement a transfer_one() operation. It provides
* standard handling of delays and chip select management.
*/
static int spi_transfer_one_message(struct spi_controller *ctlr,
struct spi_message *msg)
{
struct spi_transfer *xfer;
bool keep_cs = false;
int ret = 0;
struct spi_statistics *statm = &ctlr->statistics;
struct spi_statistics *stats = &msg->spi->statistics;
spi_set_cs(msg->spi, true, false);
SPI_STATISTICS_INCREMENT_FIELD(statm, messages);
SPI_STATISTICS_INCREMENT_FIELD(stats, messages);
list_for_each_entry(xfer, &msg->transfers, transfer_list) {
trace_spi_transfer_start(msg, xfer);
spi_statistics_add_transfer_stats(statm, xfer, ctlr);
spi_statistics_add_transfer_stats(stats, xfer, ctlr);
if (!ctlr->ptp_sts_supported) {
xfer->ptp_sts_word_pre = 0;
ptp_read_system_prets(xfer->ptp_sts);
}
if ((xfer->tx_buf || xfer->rx_buf) && xfer->len) {
reinit_completion(&ctlr->xfer_completion);
fallback_pio:
ret = ctlr->transfer_one(ctlr, msg->spi, xfer);
if (ret < 0) {
if (ctlr->cur_msg_mapped &&
(xfer->error & SPI_TRANS_FAIL_NO_START)) {
__spi_unmap_msg(ctlr, msg);
ctlr->fallback = true;
xfer->error &= ~SPI_TRANS_FAIL_NO_START;
goto fallback_pio;
}
SPI_STATISTICS_INCREMENT_FIELD(statm,
errors);
SPI_STATISTICS_INCREMENT_FIELD(stats,
errors);
dev_err(&msg->spi->dev,
"SPI transfer failed: %d\n", ret);
goto out;
}
if (ret > 0) {
ret = spi_transfer_wait(ctlr, msg, xfer);
if (ret < 0)
msg->status = ret;
}
} else {
if (xfer->len)
dev_err(&msg->spi->dev,
"Bufferless transfer has length %u\n",
xfer->len);
}
if (!ctlr->ptp_sts_supported) {
ptp_read_system_postts(xfer->ptp_sts);
xfer->ptp_sts_word_post = xfer->len;
}
trace_spi_transfer_stop(msg, xfer);
if (msg->status != -EINPROGRESS)
goto out;
spi_transfer_delay_exec(xfer);
if (xfer->cs_change) {
if (list_is_last(&xfer->transfer_list,
&msg->transfers)) {
keep_cs = true;
} else {
spi_set_cs(msg->spi, false, false);
_spi_transfer_cs_change_delay(msg, xfer);
spi_set_cs(msg->spi, true, false);
}
}
msg->actual_length += xfer->len;
}
out:
if (ret != 0 || !keep_cs)
spi_set_cs(msg->spi, false, false);
if (msg->status == -EINPROGRESS)
msg->status = ret;
if (msg->status && ctlr->handle_err)
ctlr->handle_err(ctlr, msg);
spi_finalize_current_message(ctlr);
return ret;
}spi slave 和 master 区别
master 是主动发送数据，slave 是被动接收数据（先填充数据，等待传输）
master 的 SS、SCK 是输出引脚，slave 的是输入引脚
slave 要使能接收中断，有数据来了会触发中断
