Day6: platformDriver-2

原创已于 2023-03-12 15:52:38 修改 · 420 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#linux #驱动开发

于 2023-03-12 15:47:24 首次发布

Linux 同时被 3 个专栏收录

35 篇文章

订阅专栏

device tree

3 篇文章

订阅专栏

i2c

2 篇文章

订阅专栏

文章详细阐述了Linux内核中I2C驱动的工作原理，包括I2C控制器驱动如何基于平台驱动展开，I2CAdapter的作用以及I2CSlaveDriver的实现方式。I2CControllerDriver通过platform_driver接口与设备树匹配，probe函数用于初始化控制器。I2CAdapter提供与I2C总线交互的算法，而I2CSlaveDriver则抽象了I2C从设备的驱动功能。

Platform Driver (2) – I2C Driver

在上文中说到，Linux kernel中大部分设备可以归结为平台设备，因此大部分的驱动是平台驱动（patform driver）

而对于I2C控制器，其挂载在platform Bus上，因此我们在linux kernel中常说的I2C driver，都是指I2C controller driver，都是以platform driver的形式存在，当然，对应的控制器是platform device。

与此同时，kernel抽象出I2C bus（/sys/bus/i2c），用于挂载和I2C controller通过I2C总线连接的各个I2C slave device。

本篇从窝窝科技很好的剖析i2c驱动的帖子入手学习i2c驱动架构。并理解和回答如下问题

I2C Controller Driver是如何基于platform driver展开的
为什么需要I2C Adapter， I2C Adapter提供了什么？
I2C Slave Driver是如何实现的?

I2C 硬件总线拓扑

设想一个智能家居中控屏带有LCD大屏和电容触摸屏。其电容触摸屏，加速度传感器（横竖屏）等有可能即是i2C接口。
上文中，我们将SOC外设抽象为platform bus上的platform 设备。处理器i2c controller作为master，i2c总线上的触摸屏和传感器为从设备（i2C slaves）。则进一步抽象为下图

请添加图片描述

note：在参考的窝窝科技的文档里面也提到了，linux不支持I2C外设作为i2c slave设备。但是绝大数的跑linux系统的处理器应该都是作为主设备的。

linux kernel I2C framework

上图的硬件拓扑在i2c framework中又是如何抽象的呢？
请添加图片描述

/sys/bus/i2c/devices/<0>-<1>/

where <0> is the bus the chip is connected to (e. g. i2c-0)

and <1> the chip address

例子：

pi@raspberrypi:/sys/bus/platform/devices/3f804000.i2c $ ls
driver  driver_override  i2c-1  modalias  of_node  power  subsystem  uevent

i2c Framework 框架图

代码位于路径drivers\i2c\

请添加图片描述

I2C core使用I2C adapter和I2C algorithm两个子模块抽象I2C controller的功能，使用I2C client和I2C driver抽象I2C slave device的功能（对应设备模型中的device和device driver）。另外，基于I2C协议，通过smbus模块实现SMBus（System Management Bus，系统管理总线）的功能。
I2C busses是各个I2C controller drivers的集合，位于drivers/i2c/busses/目录下，驱动工程师常说的“I2C driver”就是指它们。比如树莓派的i2C驱动：busses\i2c-bcm2835.c

I2C Controller Driver

上节中提到了，I2C busses是各个I2C controller drivers的集合，位于drivers/i2c/busses/目录下，驱动工程师常说的“I2C driver”就是指它们。比如树莓派的i2C驱动：busses\i2c-bcm2835.c。
注意这里的driver 和i2C core 框图里面的driver的区别。

请添加图片描述

参照上文中的platform驱动开发框架，

模块的入口和出口
platform driver三要素
- struct platform_driver变量
- probe/remove函数
- 用于和device tree匹配的match table

其中“模块的入口和出口”，由宏 module_platform_driver(bcm2835_i2c_driver);定义。

三要素中的“match table"函数

//driver中match table
static const struct of_device_id bcm2835_i2c_of_match[] = {
	{ .compatible = "brcm,bcm2835-i2c" },
	{},
};

//dts 中 i2c0 controller资源
		i2c0: i2c@20205000 {
			compatible = "brcm,bcm2835-i2c";
			reg = <0x7e205000 0x1000>;
			interrupts = <2 21>;
			clocks = <&clk_i2c>;
			#address-cells = <1>;
			#size-cells = <0>;
			status = "disabled";
		};

三要素中的“probe"函数

bcm2835_i2c_probe

 
static int bcm2835_i2c_probe(struct platform_device *pdev)
{
	struct bcm2835_i2c_dev *i2c_dev;
	struct resource *mem, *irq;
	u32 bus_clk_rate, divider;
	int ret;
	struct i2c_adapter *adap;
	i2c_dev = devm_kzalloc(&pdev->dev, sizeof(*i2c_dev), GFP_KERNEL);
	if (!i2c_dev)
		return -ENOMEM;
	platform_set_drvdata(pdev, i2c_dev);
	i2c_dev->dev = &pdev->dev;
	init_completion(&i2c_dev->completion);
	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	i2c_dev->regs = devm_ioremap_resource(&pdev->dev, mem);
	if (IS_ERR(i2c_dev->regs))
		return PTR_ERR(i2c_dev->regs);
	i2c_dev->clk = devm_clk_get(&pdev->dev, NULL);
	if (IS_ERR(i2c_dev->clk)) {
		dev_err(&pdev->dev, "Could not get clock\n");
		return PTR_ERR(i2c_dev->clk);
	}
	ret = of_property_read_u32(pdev->dev.of_node, "clock-frequency",
				   &bus_clk_rate);
	if (ret < 0) {
		dev_warn(&pdev->dev,
			 "Could not read clock-frequency property\n");
		bus_clk_rate = 100000;
	}
	divider = DIV_ROUND_UP(clk_get_rate(i2c_dev->clk), bus_clk_rate);
	/*
	 * Per the datasheet, the register is always interpreted as an even
	 * number, by rounding down. In other words, the LSB is ignored. So,
	 * if the LSB is set, increment the divider to avoid any issue.
	 */
	if (divider & 1)
		divider++;
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DIV, divider);
	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
	if (!irq) {
		dev_err(&pdev->dev, "No IRQ resource\n");
		return -ENODEV;
	}
	i2c_dev->irq = irq->start;
	ret = request_irq(i2c_dev->irq, bcm2835_i2c_isr, IRQF_SHARED,
			  dev_name(&pdev->dev), i2c_dev);
	if (ret) {
		dev_err(&pdev->dev, "Could not request IRQ\n");
		return -ENODEV;
	}
	adap = &i2c_dev->adapter;
	i2c_set_adapdata(adap, i2c_dev);
	adap->owner = THIS_MODULE;
	adap->class = I2C_CLASS_DEPRECATED;
	strlcpy(adap->name, "bcm2835 I2C adapter", sizeof(adap->name));
	adap->algo = &bcm2835_i2c_algo;
	adap->dev.parent = &pdev->dev;
	adap->dev.of_node = pdev->dev.of_node;
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, 0);
	ret = i2c_add_adapter(adap);
	if (ret)
		free_irq(i2c_dev->irq, i2c_dev);
	return ret;
}

我们发现其实和上文中的serial driver干了类似的事情
请添加图片描述

回忆一下上文中的serial driver:

定义并注册uart driver
注册uart port
定义并实现uart ops
这里的i2C driver（注意是图中的i2c buses）应该也是完成的类似的实现，只是不同于serial driver，这里又封装了个"adapter". 在上面的probe函数中，最终是添加了一个"adapter"

	adap = &i2c_dev->adapter;
	i2c_set_adapdata(adap, i2c_dev);
	adap->owner = THIS_MODULE;
	adap->class = I2C_CLASS_DEPRECATED;
	strlcpy(adap->name, "bcm2835 I2C adapter", sizeof(adap->name));
	adap->algo = &bcm2835_i2c_algo;
	adap->dev.parent = &pdev->dev;
	adap->dev.of_node = pdev->dev.of_node;

	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, 0);

	ret = i2c_add_adapter(adap);

这个adapter最终实现了底层的驱动

static const struct i2c_algorithm bcm2835_i2c_algo = {
	.master_xfer	= bcm2835_i2c_xfer,
	.functionality	= bcm2835_i2c_func,
};

//probe函数中：
    //注册收发中断
	ret = request_irq(i2c_dev->irq, bcm2835_i2c_isr, IRQF_SHARED,
			  dev_name(&pdev->dev), i2c_dev);
    //给adapter的algo赋值
	adap->algo = &bcm2835_i2c_algo;

i2c core

上节中提到，I2C core使用I2C adapter和I2C algorithm两个子模块抽象I2C controller的功能，使用I2C client和I2C driver抽象I2C slave device的功能（对应设备模型中的device和device driver）。
这里的driver是i2c设备driver。

i2c driver

/**
 * struct i2c_driver - represent an I2C device driver
 * @class: What kind of i2c device we instantiate (for detect)
 * @attach_adapter: Callback for bus addition (deprecated)
 * @probe: Callback for device binding
 * @remove: Callback for device unbinding
 * @shutdown: Callback for device shutdown
 * @alert: Alert callback, for example for the SMBus alert protocol
 * @command: Callback for bus-wide signaling (optional)
 * @driver: Device driver model driver
 * @id_table: List of I2C devices supported by this driver
 * @detect: Callback for device detection
 * @address_list: The I2C addresses to probe (for detect)
 * @clients: List of detected clients we created (for i2c-core use only)
 *
 * The driver.owner field should be set to the module owner of this driver.
 * The driver.name field should be set to the name of this driver.
 *
 * For automatic device detection, both @detect and @address_list must
 * be defined. @class should also be set, otherwise only devices forced
 * with module parameters will be created. The detect function must
 * fill at least the name field of the i2c_board_info structure it is
 * handed upon successful detection, and possibly also the flags field.
 *
 * If @detect is missing, the driver will still work fine for enumerated
 * devices. Detected devices simply won't be supported. This is expected
 * for the many I2C/SMBus devices which can't be detected reliably, and
 * the ones which can always be enumerated in practice.
 *
 * The i2c_client structure which is handed to the @detect callback is
 * not a real i2c_client. It is initialized just enough so that you can
 * call i2c_smbus_read_byte_data and friends on it. Don't do anything
 * else with it. In particular, calling dev_dbg and friends on it is
 * not allowed.
 */
struct i2c_driver {
	unsigned int class;

	/* Notifies the driver that a new bus has appeared. You should avoid
	 * using this, it will be removed in a near future.
	 */
	int (*attach_adapter)(struct i2c_adapter *) __deprecated;

	/* Standard driver model interfaces */
	int (*probe)(struct i2c_client *, const struct i2c_device_id *);
	int (*remove)(struct i2c_client *);

	/* driver model interfaces that don't relate to enumeration  */
	void (*shutdown)(struct i2c_client *);

	/* Alert callback, for example for the SMBus alert protocol.
	 * The format and meaning of the data value depends on the protocol.
	 * For the SMBus alert protocol, there is a single bit of data passed
	 * as the alert response's low bit ("event flag").
	 */
	void (*alert)(struct i2c_client *, unsigned int data);

	/* a ioctl like command that can be used to perform specific functions
	 * with the device.
	 */
	int (*command)(struct i2c_client *client, unsigned int cmd, void *arg);

	struct device_driver driver;
	const struct i2c_device_id *id_table;

	/* Device detection callback for automatic device creation */
	int (*detect)(struct i2c_client *, struct i2c_board_info *);
	const unsigned short *address_list;
	struct list_head clients;
};

I2C adapter

/*
 * i2c_adapter is the structure used to identify a physical i2c bus along
 * with the access algorithms necessary to access it.
 */
struct i2c_adapter {
	struct module *owner;
	unsigned int class;		  /* classes to allow probing for */
	const struct i2c_algorithm *algo; /* the algorithm to access the bus */
	void *algo_data;

	/* data fields that are valid for all devices	*/
	struct rt_mutex bus_lock;

	int timeout;			/* in jiffies */
	int retries;
	struct device dev;		/* the adapter device */

	int nr;
	char name[48];
	struct completion dev_released;

	struct mutex userspace_clients_lock;
	struct list_head userspace_clients;

	struct i2c_bus_recovery_info *bus_recovery_info;
	const struct i2c_adapter_quirks *quirks;
};

I2C Client

/**
 * struct i2c_client - represent an I2C slave device
 * @flags: I2C_CLIENT_TEN indicates the device uses a ten bit chip address;
 *	I2C_CLIENT_PEC indicates it uses SMBus Packet Error Checking
 * @addr: Address used on the I2C bus connected to the parent adapter.
 * @name: Indicates the type of the device, usually a chip name that's
 *	generic enough to hide second-sourcing and compatible revisions.
 * @adapter: manages the bus segment hosting this I2C device
 * @dev: Driver model device node for the slave.
 * @irq: indicates the IRQ generated by this device (if any)
 * @detected: member of an i2c_driver.clients list or i2c-core's
 *	userspace_devices list
 * @slave_cb: Callback when I2C slave mode of an adapter is used. The adapter
 *	calls it to pass on slave events to the slave driver.
 *
 * An i2c_client identifies a single device (i.e. chip) connected to an
 * i2c bus. The behaviour exposed to Linux is defined by the driver
 * managing the device.
 */
struct i2c_client {
	unsigned short flags;		/* div., see below		*/
	unsigned short addr;		/* chip address - NOTE: 7bit	*/
					/* addresses are stored in the	*/
					/* _LOWER_ 7 bits		*/
	char name[I2C_NAME_SIZE];
	struct i2c_adapter *adapter;	/* the adapter we sit on	*/
	struct device dev;		/* the device structure		*/
	int irq;			/* irq issued by device		*/
	struct list_head detected;
#if IS_ENABLED(CONFIG_I2C_SLAVE)
	i2c_slave_cb_t slave_cb;	/* callback for slave mode	*/
#endif
};

下文再接着看如何基于kernel提供的i2c framework，在内核空间或者用户空间开发i2c 设备驱动（device driver）

请添加图片描述

#参考
http://www.wowotech.net/comm/i2c_overview.html
http://www.wowotech.net/comm/i2c_provider.html
http://www.wowotech.net/comm/i2c_consumer.html

https://www.kernel.org/doc/Documentation/hwmon/pcf8591
https://blog.youkuaiyun.com/feiwatson/article/details/81048616?spm=1001.2014.3001.5501
空间或者用户空间开发i2c 设备驱动（device driver）

[外链图片转存中…(img-0pSbOJa4-1678606364666)]

#参考
http://www.wowotech.net/comm/i2c_overview.html
http://www.wowotech.net/comm/i2c_provider.html
http://www.wowotech.net/comm/i2c_consumer.html

https://www.kernel.org/doc/Documentation/hwmon/pcf8591
https://blog.youkuaiyun.com/feiwatson/article/details/81048616?spm=1001.2014.3001.5501