设备是设备,驱动是驱动。node
若是把两个糅合写一块儿,当设备发生变化时,势必要改写整个文件,这是很是愚蠢的作法。若是把他们分开来,当设备发生变化时,只要改写设备文件便可,驱动文件巍然不动。linux
从linux2.6内核起,引入一套新的驱动管理和注册机制:platform_device 和 platform_driver 。Linux 中大部分的设备驱动,均可以使用这套机制,设备用 platform_device 表示;驱动用 platform_driver 进行注册。app
platform将驱动分为platform_device (设备文件)和platform_driver(驱动文件),他们会经过platform总线来相配对。当设备注册到总线时,会经过总线去寻找有没有相对应的驱动文件,有的话则将他两配对。同理,当驱动注册到总线时,会经过总线去寻找有没有相对应的设备文件,有的话也将他两进行配对。dom
linux platform driver 机制和传统的device driver机制(即:经过 driver_register 函数进行注册)相比,一个十分明显的优点在于platform机制将设备自己的资源注册进内核,由内核统一管理,在驱动程序中用使用这些资源时,经过platform device提供的标准接口进行申请并使用。async
以kernel 4.8.17为例,驱动文件:ide
platform_driver_register(&led_drv); ——>__platform_driver_register ——>drv->driver.bus = &platform_bus_type; ——>.match = platform_match, ——>of_driver_match_device(dev, drv) ——>of_match_device(drv->of_match_table, dev) ——>of_match_node(matches, dev->of_node) ——>__of_match_node(matches, node) ——>__of_device_is_compatible(node, matches->compatible,matches->type, matches->name) ——>acpi_driver_match_device(dev, drv) ——>platform_match_id(pdrv->id_table, pdev) ——>strcmp(pdev->name, drv->name)
代码如上,驱动注册时,会在总线上与设备匹配,有四种匹配方法:函数
1)如5行,经过这个OpenFirmware的匹配方式,匹配name、type、和compatible字符串三个属性,三者要同时相同(通常name、和type为空,只比较compatible字符串),compatible这个好像是在设备树(dts)里说到,这个以后再讨论。若是不匹配,则会进行第二种匹配方式。学习
2)如11行,我也不知道这个acpi_driver_match_device是什么,反正也是若是不匹配,则会进行第三种匹配方式。this
3)如12行,经过id_table方式匹配,比较设备的名字和id_table里的名字是否有相同的。这样在id_table能够实现一个驱动对应多个设备。若是没有,则会进行第四种匹配方式了。atom
4)如13行,直接比较设备名字和驱动名字。
即便匹配不成功,也会driver_register(&drv->driver)进行注册,等带设备注册时来与驱动匹配。
若是匹配成功,则会引起驱动的probe()函数执行。
设备文件:
platform_device_register(&led_dev) platform_device_add(pdev) pdev->dev.bus = &platform_bus_type .match = platform_match /*以后就同样了*/
那么他们具体是怎么操做的呢?咱们来具体分析,以platform_device_register为例:
int platform_device_register(struct platform_device *pdev) { device_initialize(&pdev->dev); arch_setup_pdev_archdata(pdev); return platform_device_add(pdev); }
这里面,先初始化device,其中涉及kset,能够看看这篇文章:嵌入式Linux驱动学习笔记(十六)------设备驱动模型(kobject、kset、ktype)
而后是platform_device_add函数:
int platform_device_add(struct platform_device *pdev) { int i, ret; if (!pdev) return -EINVAL; if (!pdev->dev.parent) pdev->dev.parent = &platform_bus; pdev->dev.bus = &platform_bus_type; switch (pdev->id) { default: dev_set_name(&pdev->dev, "%s.%d", pdev->name, pdev->id); break; case PLATFORM_DEVID_NONE: dev_set_name(&pdev->dev, "%s", pdev->name); break; case PLATFORM_DEVID_AUTO: ret = ida_simple_get(&platform_devid_ida, 0, 0, GFP_KERNEL); if (ret < 0) goto err_out; pdev->id = ret; pdev->id_auto = true; dev_set_name(&pdev->dev, "%s.%d.auto", pdev->name, pdev->id); break; } for (i = 0; i < pdev->num_resources; i++) { struct resource *p, *r = &pdev->resource[i]; if (r->name == NULL) r->name = dev_name(&pdev->dev); p = r->parent; if (!p) { if (resource_type(r) == IORESOURCE_MEM) p = &iomem_resource; else if (resource_type(r) == IORESOURCE_IO) p = &ioport_resource; } if (p && insert_resource(p, r)) { dev_err(&pdev->dev, "failed to claim resource %d\n", i); ret = -EBUSY; goto failed; } } pr_debug("Registering platform device '%s'. Parent at %s\n", dev_name(&pdev->dev), dev_name(pdev->dev.parent)); ret = device_add(&pdev->dev); if (ret == 0) return ret; /*省略部分代码*/ }
这里面,这是了所属总线,填充好名字,就会调用device_add函数了,
这个函数也很复杂,我放在嵌入式Linux驱动笔记(十六)------设备驱动模型(kobject、kset、ktype)这里讲了
可是,复杂的那些细节咱们咱们先能够不看,咱们看到device_add函数里调用bus_probe_device函数,这一个探测函数:
void bus_probe_device(struct device *dev) { struct bus_type *bus = dev->bus; struct subsys_interface *sif; if (!bus) return; if (bus->p->drivers_autoprobe)//设置了自动匹配初始化那么就开始匹配 device_initial_probe(dev); mutex_lock(&bus->p->mutex); list_for_each_entry(sif, &bus->p->interfaces, node) if (sif->add_dev) sif->add_dev(dev, sif); mutex_unlock(&bus->p->mutex); }
这里面,调用了device_initial_probe函数,device_initial_probe又调用了__device_attach函数,咱们继续看看:
static int __device_attach(struct device *dev, bool allow_async) { int ret = 0; device_lock(dev); if (dev->driver) { if (device_is_bound(dev)) { ret = 1; goto out_unlock; } ret = device_bind_driver(dev); if (ret == 0) ret = 1; else { dev->driver = NULL; ret = 0; } } else { struct device_attach_data data = { .dev = dev, .check_async = allow_async, .want_async = false, }; if (dev->parent) pm_runtime_get_sync(dev->parent); ret = bus_for_each_drv(dev->bus, NULL, &data, __device_attach_driver); if (!ret && allow_async && data.have_async) { dev_dbg(dev, "scheduling asynchronous probe\n"); get_device(dev); async_schedule(__device_attach_async_helper, dev); } else { pm_request_idle(dev); } if (dev->parent) pm_runtime_put(dev->parent); } out_unlock: device_unlock(dev); return ret; }
函数一开始,先检查device是否绑定过了,接着调用device_bind_driver对device和driver进行绑定:
int device_bind_driver(struct device *dev) { int ret; ret = driver_sysfs_add(dev);//将driver和dev使用link,连接到一块儿,使他们真正相关 if (!ret) driver_bound(dev);//将私有成员的driver节点挂到了driver的设备链表 else if (dev->bus) blocking_notifier_call_chain(&dev->bus->p->bus_notifier, BUS_NOTIFY_DRIVER_NOT_BOUND, dev);//通知bus上全部设备bound消息 return ret; }
static int driver_sysfs_add(struct device *dev) { int ret; if (dev->bus) blocking_notifier_call_chain(&dev->bus->p->bus_notifier, BUS_NOTIFY_BIND_DRIVER, dev); ret = sysfs_create_link(&dev->driver->p->kobj, &dev->kobj, kobject_name(&dev->kobj));//驱动目录下dev->kobj目录连接到dev->kobj if (ret == 0) { ret = sysfs_create_link(&dev->kobj, &dev->driver->p->kobj, "driver");//在dev->kobj目录下的driver目录连接到其驱动目录 if (ret) sysfs_remove_link(&dev->driver->p->kobj, kobject_name(&dev->kobj)); } return ret; }
接着调用__device_attach_driver进行match:
static int __device_attach_driver(struct device_driver *drv, void *_data) { struct device_attach_data *data = _data; struct device *dev = data->dev; bool async_allowed; int ret; /* * Check if device has already been claimed. This may * happen with driver loading, device discovery/registration, * and deferred probe processing happens all at once with * multiple threads. */ if (dev->driver) return -EBUSY; ret = driver_match_device(drv, dev); if (ret == 0) { /* no match */ return 0; } else if (ret == -EPROBE_DEFER) { dev_dbg(dev, "Device match requests probe deferral\n"); driver_deferred_probe_add(dev); } else if (ret < 0) { dev_dbg(dev, "Bus failed to match device: %d", ret); return ret; } /* ret > 0 means positive match */ async_allowed = driver_allows_async_probing(drv); if (async_allowed) data->have_async = true; if (data->check_async && async_allowed != data->want_async) return 0; return driver_probe_device(drv, dev); }
这里面,先调用driver_match_device进行各类关键字match:
static inline int driver_match_device(struct device_driver *drv, struct device *dev) { return drv->bus->match ? drv->bus->match(dev, drv) : 1; }
而后就是调用driver_probe_device函数触发probe函数:
int driver_probe_device(struct device_driver *drv, struct device *dev) { int ret = 0; if (!device_is_registered(dev)) return -ENODEV; pr_debug("bus: '%s': %s: matched device %s with driver %s\n", drv->bus->name, __func__, dev_name(dev), drv->name); if (dev->parent) pm_runtime_get_sync(dev->parent); pm_runtime_barrier(dev); ret = really_probe(dev, drv);//调用really_probe pm_request_idle(dev); if (dev->parent) pm_runtime_put(dev->parent); return ret; }
函数一开始检查device是否注册过,若是注册过,直接return。
不然,则调用really_probe函数:
static int really_probe(struct device *dev, struct device_driver *drv) { int ret = -EPROBE_DEFER; int local_trigger_count = atomic_read(&deferred_trigger_count); if (defer_all_probes) { /* * Value of defer_all_probes can be set only by * device_defer_all_probes_enable() which, in turn, will call * wait_for_device_probe() right after that to avoid any races. */ dev_dbg(dev, "Driver %s force probe deferral\n", drv->name); driver_deferred_probe_add(dev); return ret; } atomic_inc(&probe_count); pr_debug("bus: '%s': %s: probing driver %s with device %s\n", drv->bus->name, __func__, drv->name, dev_name(dev)); WARN_ON(!list_empty(&dev->devres_head)); dev->driver = drv; /* If using pinctrl, bind pins now before probing */ ret = pinctrl_bind_pins(dev); if (ret) goto pinctrl_bind_failed; if (driver_sysfs_add(dev)) {//驱动目录下创建一个到设备的同名连接,而且在设备目录下创建一个名为 driver.到驱动的连接 printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n", __func__, dev_name(dev)); goto probe_failed; } if (dev->pm_domain && dev->pm_domain->activate) { ret = dev->pm_domain->activate(dev); if (ret) goto probe_failed; } /* * Ensure devices are listed in devices_kset in correct order * It's important to move Dev to the end of devices_kset before * calling .probe, because it could be recursive and parent Dev * should always go first */ devices_kset_move_last(dev); if (dev->bus->probe) { ret = dev->bus->probe(dev);//若是bus的probe存在就用bus的 if (ret) goto probe_failed; } else if (drv->probe) {//若是bus的不存在driver的存在 ret = drv->probe(dev);//再用driver的 if (ret) goto probe_failed; } pinctrl_init_done(dev); if (dev->pm_domain && dev->pm_domain->sync) dev->pm_domain->sync(dev); driver_bound(dev);//调用driver_bound进行绑定 ret = 1; pr_debug("bus: '%s': %s: bound device %s to driver %s\n", drv->bus->name, __func__, dev_name(dev), drv->name); goto done; /*省略部分代码*/ }
这里,先调用driver_sysfs_add函数,把drivers添加到sysfs中:
static int driver_sysfs_add(struct device *dev) { int ret; if (dev->bus) blocking_notifier_call_chain(&dev->bus->p->bus_notifier, BUS_NOTIFY_BIND_DRIVER, dev); ret = sysfs_create_link(&dev->driver->p->kobj, &dev->kobj, kobject_name(&dev->kobj));//驱动目录下dev->kobj目录连接到dev->kobj if (ret == 0) { ret = sysfs_create_link(&dev->kobj, &dev->driver->p->kobj, "driver");//在dev->kobj目录下的driver目录连接到其驱动目录 if (ret) sysfs_remove_link(&dev->driver->p->kobj, kobject_name(&dev->kobj)); } return ret; }
最后,也是咱们指望看到的,probe函数的触发:
if (dev->bus->probe) { ret = dev->bus->probe(dev);//若是bus的probe存在就用bus的 if (ret) goto probe_failed; } else if (drv->probe) {//若是bus的不存在driver的存在 ret = drv->probe(dev);//再用driver的 if (ret) goto probe_failed; }
咱们的platform总线是不自带probe的,因此这里对触发drv->probe,好了,分析到这里,就大功告成了!
platform_driver_register函数也是同样的分析方法,就很少累述了。
因此咱们主要仍是 构造好这platform_driver个驱动结构体,结构体原型为:
struct platform_driver { int (*probe)(struct platform_device *);/*匹配成功以后调用该函数*/ int (*remove)(struct platform_device *); /*卸载了调用该函数*/ void (*shutdown)(struct platform_device *); int (*suspend)(struct platform_device *, pm_message_t state); int (*resume)(struct platform_device *); struct device_driver driver; /*内核里全部的驱动程序必须包含该结构体*/ const struct platform_device_id *id_table; bool prevent_deferred_probe; };
设备的结构体为:
struct platform_device { const char *name; /*名字*/ int id; bool id_auto; struct device dev; /*硬件模块必须包含该结构体*/ u32 num_resources; /*资源个数*/ struct resource *resource; /*资源*/ const struct platform_device_id *id_entry; char *driver_override; /* Driver name to force a match */ /* MFD cell pointer */ struct mfd_cell *mfd_cell; /* arch specific additions */ struct pdev_archdata archdata; };
其中,有个重要的参数:resource(资源),结构体以下 :
struct resource { resource_size_t start;/*资源的起始地址*/ resource_size_t end;/*资源的结束地址*/ const char *name;/*资源的名字*/ unsigned long flags;/*资源的类型*/ unsigned long desc; struct resource *parent, *sibling, *child; };
flags类型的可选参数有:
IORESOURCE_TYPE_BITS
IORESOURCE_IO/*IO地址空间*/
IORESOURCE_MEM/*属于外设或者用于和设备通信的支持直接寻址的地址空间*/
IORESOURCE_REG/*寄存器偏移量*/
IORESOURCE_IRQ
IORESOURCE_DMA
IORESOURCE_BUS
start、end的含义会随着flags而变动,如:
当flags为IORESOURCE_MEM时,start、end分别表示该platform_device占据的内存的开始地址和结束地址;
当flags为IORESOURCE_IRQ时,start、end分别表示该platform_device使用的中断号的开始值和结束值,若是只使用了1个中断号,开始和结束值相同。
对于同种类型的资源而言,能够有多份,譬如说某设备占据了2个内存区域,则能够定义2个IORESOURCE_MEM资源。
下面给出完整程序参考,摘抄自韦东山驱动视频。
驱动文件:
/* 分配/设置/注册一个platform_driver */ #include <linux/module.h> #include <linux/version.h> #include <linux/init.h> #include <linux/fs.h> #include <linux/interrupt.h> #include <linux/irq.h> #include <linux/sched.h> #include <linux/pm.h> #include <linux/sysctl.h> #include <linux/proc_fs.h> #include <linux/delay.h> #include <linux/platform_device.h> #include <linux/input.h> #include <linux/irq.h> #include <asm/uaccess.h> #include <asm/io.h> static int major; static struct class *cls; static volatile unsigned long *gpio_con; static volatile unsigned long *gpio_dat; static int pin; static int led_open(struct inode *inode, struct file *file) { /* 配置为输出 */ *gpio_con &= ~(0x3<<(pin*2)); *gpio_con |= (0x1<<(pin*2)); return 0; } static ssize_t led_write(struct file *file, const char __user *buf, size_t count, loff_t * ppos) { int val; copy_from_user(&val, buf, count); // copy_to_user(); if (val == 1) { // 点灯 *gpio_dat &= ~(1<<pin); } else { // 灭灯 *gpio_dat |= (1<<pin); } return 0; } static struct file_operations led_fops = { .owner = THIS_MODULE, /* 这是一个宏,推向编译模块时自动建立的__this_module变量 */ .open = led_open, .write = led_write, }; static int led_probe(struct platform_device *pdev) { struct resource *res; /* 根据platform_device的资源进行ioremap */ res = platform_get_resource(pdev, IORESOURCE_MEM, 0); gpio_con = ioremap(res->start, res->end - res->start + 1); gpio_dat = gpio_con + 1; res = platform_get_resource(pdev, IORESOURCE_IRQ, 0); pin = res->start; /* 注册字符设备驱动程序 */ printk("led_probe, found led\n"); major = register_chrdev(0, "myled", &led_fops); cls = class_create(THIS_MODULE, "myled"); //class_device_create(cls, NULL, MKDEV(major, 0), NULL, "led"); /* /dev/led */ device_create(cls, NULL, MKDEV(major, 0), NULL, "led"); /* /dev/led */ return 0; } static int led_remove(struct platform_device *pdev) { /* 卸载字符设备驱动程序 */ /* iounmap */ printk("led_remove, remove led\n"); //class_device_destroy(cls, MKDEV(major, 0)); device_destroy(cls, MKDEV(major, 0)); class_destroy(cls); unregister_chrdev(major, "myled"); iounmap(gpio_con); return 0; } struct platform_driver led_drv = { .probe = led_probe, .remove = led_remove, .driver = { .name = "myled", } }; static int led_drv_init(void) { platform_driver_register(&led_drv); return 0; } static void led_drv_exit(void) { platform_driver_unregister(&led_drv); } module_init(led_drv_init); module_exit(led_drv_exit); MODULE_LICENSE("GPL");
设备文件:
/* 分配/设置/注册一个platform_device */ #include <linux/module.h> #include <linux/version.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/types.h> #include <linux/interrupt.h> #include <linux/list.h> #include <linux/timer.h> #include <linux/init.h> #include <linux/serial_core.h> #include <linux/platform_device.h> static struct resource led_resource[] = { [0] = { .start = 0x56000050, .end = 0x56000050 + 8 - 1, .flags = IORESOURCE_MEM,/*指的是属于外设或者用于和设备通信的支持直接寻址的地址空间*/ }, [1] = { .start = 5, .end = 5, .flags = IORESOURCE_IRQ, } }; static void led_release(struct device * dev) { } static struct platform_device led_dev = { .name = "myled", .id = -1, .num_resources = ARRAY_SIZE(led_resource),/*资源个数*/ .resource = led_resource, .dev = { .release = led_release, }, }; static int led_dev_init(void) { platform_device_register(&led_dev); return 0; } static void led_dev_exit(void) { platform_device_unregister(&led_dev); } module_init(led_dev_init); module_exit(led_dev_exit); MODULE_LICENSE("GPL");
须要注意的是:platform_driver 和 platform_device 中的 name 变量的值必须是相同的 。这样在 platform_driver_register() 注册时,会将当前注册的 platform_driver 中的 name 变量的值和已注册的全部 platform_device 中的 name 变量的值进行比较,只有找到具备相同名称的 platform_device 才能注册成功。当注册成功时,会调用 platform_driver 结构元素 probe 函数指针,运行.probe进行初始化。
最后,结合十六节文章分析口味更佳!