設備是設備,驅動是驅動。node
若是把兩個糅合寫一塊兒,當設備發生變化時,勢必要改寫整個文件,這是很是愚蠢的作法。若是把他們分開來,當設備發生變化時,只要改寫設備文件便可,驅動文件巍然不動。linux
從linux2.6內核起,引入一套新的驅動管理和註冊機制:platform_device 和 platform_driver 。Linux 中大部分的設備驅動,均可以使用這套機制,設備用 platform_device 表示;驅動用 platform_driver 進行註冊。app
platform將驅動分爲platform_device (設備文件)和platform_driver(驅動文件),他們會經過platform總線來相配對。當設備註冊到總線時,會經過總線去尋找有沒有相對應的驅動文件,有的話則將他兩配對。同理,當驅動註冊到總線時,會經過總線去尋找有沒有相對應的設備文件,有的話也將他兩進行配對。dom
linux platform driver 機制和傳統的device driver機制(即:經過 driver_register 函數進行註冊)相比,一個十分明顯的優點在於platform機制將設備自己的資源註冊進內核,由內核統一管理,在驅動程序中用使用這些資源時,經過platform device提供的標準接口進行申請並使用。async
以kernel 4.8.17爲例,驅動文件: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)
代碼如上,驅動註冊時,會在總線上與設備匹配,有四種匹配方法:函數
1)如5行,經過這個OpenFirmware的匹配方式,匹配name、type、和compatible字符串三個屬性,三者要同時相同(通常name、和type爲空,只比較compatible字符串),compatible這個好像是在設備樹(dts)裏說到,這個以後再討論。若是不匹配,則會進行第二種匹配方式。學習
2)如11行,我也不知道這個acpi_driver_match_device是什麼,反正也是若是不匹配,則會進行第三種匹配方式。this
3)如12行,經過id_table方式匹配,比較設備的名字和id_table裏的名字是否有相同的。這樣在id_table能夠實現一個驅動對應多個設備。若是沒有,則會進行第四種匹配方式了。atom
4)如13行,直接比較設備名字和驅動名字。
即便匹配不成功,也會driver_register(&drv->driver)進行註冊,等帶設備註冊時來與驅動匹配。
若是匹配成功,則會引起驅動的probe()函數執行。
設備文件:
platform_device_register(&led_dev) platform_device_add(pdev) pdev->dev.bus = &platform_bus_type .match = platform_match /*以後就同樣了*/
那麼他們具體是怎麼操做的呢?咱們來具體分析,以platform_device_register爲例:
int platform_device_register(struct platform_device *pdev) { device_initialize(&pdev->dev); arch_setup_pdev_archdata(pdev); return platform_device_add(pdev); }
這裏面,先初始化device,其中涉及kset,能夠看看這篇文章:嵌入式Linux驅動學習筆記(十六)------設備驅動模型(kobject、kset、ktype)
而後是platform_device_add函數:
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; /*省略部分代碼*/ }
這裏面,這是了所屬總線,填充好名字,就會調用device_add函數了,
這個函數也很複雜,我放在嵌入式Linux驅動筆記(十六)------設備驅動模型(kobject、kset、ktype)這裏講了
可是,複雜的那些細節咱們咱們先能夠不看,咱們看到device_add函數裏調用bus_probe_device函數,這一個探測函數:
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)//設置了自動匹配初始化那麼就開始匹配 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); }
這裏面,調用了device_initial_probe函數,device_initial_probe又調用了__device_attach函數,咱們繼續看看:
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; }
函數一開始,先檢查device是否綁定過了,接着調用device_bind_driver對device和driver進行綁定:
int device_bind_driver(struct device *dev) { int ret; ret = driver_sysfs_add(dev);//將driver和dev使用link,連接到一塊兒,使他們真正相關 if (!ret) driver_bound(dev);//將私有成員的driver節點掛到了driver的設備鏈表 else if (dev->bus) blocking_notifier_call_chain(&dev->bus->p->bus_notifier, BUS_NOTIFY_DRIVER_NOT_BOUND, dev);//通知bus上全部設備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));//驅動目錄下dev->kobj目錄連接到dev->kobj if (ret == 0) { ret = sysfs_create_link(&dev->kobj, &dev->driver->p->kobj, "driver");//在dev->kobj目錄下的driver目錄連接到其驅動目錄 if (ret) sysfs_remove_link(&dev->driver->p->kobj, kobject_name(&dev->kobj)); } return ret; }
接着調用__device_attach_driver進行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); }
這裏面,先調用driver_match_device進行各類關鍵字match:
static inline int driver_match_device(struct device_driver *drv, struct device *dev) { return drv->bus->match ? drv->bus->match(dev, drv) : 1; }
而後就是調用driver_probe_device函數觸發probe函數:
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);//調用really_probe pm_request_idle(dev); if (dev->parent) pm_runtime_put(dev->parent); return ret; }
函數一開始檢查device是否註冊過,若是註冊過,直接return。
不然,則調用really_probe函數:
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)) {//驅動目錄下創建一個到設備的同名連接,而且在設備目錄下創建一個名爲 driver.到驅動的連接 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);//調用driver_bound進行綁定 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; /*省略部分代碼*/ }
這裏,先調用driver_sysfs_add函數,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));//驅動目錄下dev->kobj目錄連接到dev->kobj if (ret == 0) { ret = sysfs_create_link(&dev->kobj, &dev->driver->p->kobj, "driver");//在dev->kobj目錄下的driver目錄連接到其驅動目錄 if (ret) sysfs_remove_link(&dev->driver->p->kobj, kobject_name(&dev->kobj)); } return ret; }
最後,也是咱們指望看到的,probe函數的觸發:
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; }
咱們的platform總線是不自帶probe的,因此這裏對觸發drv->probe,好了,分析到這裏,就大功告成了!
platform_driver_register函數也是同樣的分析方法,就很少累述了。
因此咱們主要仍是 構造好這platform_driver個驅動結構體,結構體原型爲:
struct platform_driver { int (*probe)(struct platform_device *);/*匹配成功以後調用該函數*/ int (*remove)(struct platform_device *); /*卸載了調用該函數*/ void (*shutdown)(struct platform_device *); int (*suspend)(struct platform_device *, pm_message_t state); int (*resume)(struct platform_device *); struct device_driver driver; /*內核裏全部的驅動程序必須包含該結構體*/ const struct platform_device_id *id_table; bool prevent_deferred_probe; };
設備的結構體爲:
struct platform_device { const char *name; /*名字*/ int id; bool id_auto; struct device dev; /*硬件模塊必須包含該結構體*/ u32 num_resources; /*資源個數*/ struct resource *resource; /*資源*/ 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,有個重要的參數:resource(資源),結構體以下 :
struct resource { resource_size_t start;/*資源的起始地址*/ resource_size_t end;/*資源的結束地址*/ const char *name;/*資源的名字*/ unsigned long flags;/*資源的類型*/ unsigned long desc; struct resource *parent, *sibling, *child; };
flags類型的可選參數有:
IORESOURCE_TYPE_BITS
IORESOURCE_IO/*IO地址空間*/
IORESOURCE_MEM/*屬於外設或者用於和設備通信的支持直接尋址的地址空間*/
IORESOURCE_REG/*寄存器偏移量*/
IORESOURCE_IRQ
IORESOURCE_DMA
IORESOURCE_BUS
start、end的含義會隨着flags而變動,如:
當flags爲IORESOURCE_MEM時,start、end分別表示該platform_device佔據的內存的開始地址和結束地址;
當flags爲IORESOURCE_IRQ時,start、end分別表示該platform_device使用的中斷號的開始值和結束值,若是隻使用了1箇中斷號,開始和結束值相同。
對於同種類型的資源而言,能夠有多份,譬如說某設備佔據了2個內存區域,則能夠定義2個IORESOURCE_MEM資源。
下面給出完整程序參考,摘抄自韋東山驅動視頻。
驅動文件:
/* 分配/設置/註冊一個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) { /* 配置爲輸出 */ *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) { // 點燈 *gpio_dat &= ~(1<<pin); } else { // 滅燈 *gpio_dat |= (1<<pin); } return 0; } static struct file_operations led_fops = { .owner = THIS_MODULE, /* 這是一個宏,推向編譯模塊時自動建立的__this_module變量 */ .open = led_open, .write = led_write, }; static int led_probe(struct platform_device *pdev) { struct resource *res; /* 根據platform_device的資源進行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; /* 註冊字符設備驅動程序 */ 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) { /* 卸載字符設備驅動程序 */ /* 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");
設備文件:
/* 分配/設置/註冊一個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,/*指的是屬於外設或者用於和設備通信的支持直接尋址的地址空間*/ }, [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),/*資源個數*/ .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");
須要注意的是:platform_driver 和 platform_device 中的 name 變量的值必須是相同的 。這樣在 platform_driver_register() 註冊時,會將當前註冊的 platform_driver 中的 name 變量的值和已註冊的全部 platform_device 中的 name 變量的值進行比較,只有找到具備相同名稱的 platform_device 才能註冊成功。當註冊成功時,會調用 platform_driver 結構元素 probe 函數指針,運行.probe進行初始化。
最後,結合十六節文章分析口味更佳!