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Linux之platform平臺設(shè)備驅(qū)動詳解

更新時間：2025年07月22日 15:08:22 作者：大肥周

Linux設(shè)備驅(qū)動模型中,Platform總線作為虛擬總線統(tǒng)一管理無物理總線依賴的嵌入式設(shè)備,通過platform_driver和platform_device注冊,結(jié)合設(shè)備樹的of_match_table匹配機(jī)制,實現(xiàn)驅(qū)動與設(shè)備的自動綁定,確保無論注冊順序如何均能正確觸發(fā)probe函數(shù)

platform驅(qū)動注冊

結(jié)構(gòu)體是struct platform_driver，主要包含probe、remove等接口。

struct platform_driver {
	int (*probe)(struct platform_device *);

	/*
	 * Traditionally the remove callback returned an int which however is
	 * ignored by the driver core. This led to wrong expectations by driver
	 * authors who thought returning an error code was a valid error
	 * handling strategy. To convert to a callback returning void, new
	 * drivers should implement .remove_new() until the conversion it done
	 * that eventually makes .remove() return void.
	 */
	int (*remove)(struct platform_device *);
	void (*remove_new)(struct platform_device *);

	void (*shutdown)(struct platform_device *);
	int (*suspend)(struct platform_device *, pm_message_t state);
	int (*resume)(struct platform_device *);
	struct device_driver driver;
	const struct platform_device_id *id_table;
	bool prevent_deferred_probe;
	/*
	 * For most device drivers, no need to care about this flag as long as
	 * all DMAs are handled through the kernel DMA API. For some special
	 * ones, for example VFIO drivers, they know how to manage the DMA
	 * themselves and set this flag so that the IOMMU layer will allow them
	 * to setup and manage their own I/O address space.
	 */
	bool driver_managed_dma;
};

驅(qū)動注冊接口是platform_driver_register，主要是把bus配成platform_bus_type后調(diào)用driver_register注冊。

代碼示例：

int zsl_drv_probe(struct platform_device *dev)
{
	struct property *pp = NULL;

	printk(KERN_INFO "%s: \n",__func__);

	dump_stack();  // 打印堆棧

    return 0;
}

int zsl_drv_remove(struct platform_device *dev)
{
	printk(KERN_INFO "%s: \n",__func__);
    return 0;
}

struct platform_driver zsl_drv =
{
    .driver =
    {
        .name = "zsltest",			
    },
     
    .probe = zsl_drv_probe,
    .remove = zsl_drv_remove,
};

再使用platform_driver_register(&zsl_drv)注冊這個驅(qū)動。

platform設(shè)備注冊

結(jié)構(gòu)體是struct platform_device，主要包含probe、remove等接口。

struct platform_device {
	const char	*name;
	int		id;
	bool		id_auto;
	struct device	dev;
	u64		platform_dma_mask;
	struct device_dma_parameters dma_parms;
	u32		num_resources;
	struct resource	*resource;

	const struct platform_device_id	*id_entry;
	/*
	 * Driver name to force a match.  Do not set directly, because core
	 * frees it.  Use driver_set_override() to set or clear it.
	 */
	const char *driver_override;

	/* MFD cell pointer */
	struct mfd_cell *mfd_cell;

	/* arch specific additions */
	struct pdev_archdata	archdata;
};

注冊接口是platform_device_register，主要是把設(shè)備屬性填充后，后調(diào)用device_add注冊。

代碼示例：

struct platform_device zsl_dev =
{
    .name = "zsltest",
    .dev =
    {
        .release = zsl_dev_release,
    },
};

再使用platform_device_register(&zsl_dev)注冊這個設(shè)備，其中zsl_dev里的name和zsl_drv的name保持一樣，才能讓platform device和platform driver匹配上，從而調(diào)用zsl_drv.probe。

跟platform驅(qū)動注冊配套使用后，運(yùn)行打印如下，可以看到zsl_drv.probe會被調(diào)用到。

運(yùn)行結(jié)果：

先注冊dev，再注冊drv

先注冊drv，再注冊dev

設(shè)備樹

支持設(shè)備的內(nèi)核里，更推薦使用設(shè)備樹的方式，而不是platform設(shè)備注冊的方式。

去掉zsl_dev設(shè)備的注冊代碼，在zsl_drv變量里增加.of_match_table = zsl_of_match,并且zsl_of_match表里增加.compatible = "rockchip,zslzsl",然后在設(shè)備樹里增加以下代碼。

保持兩邊的compatible一致，并且status是okay的。

這樣就會調(diào)用zsl_drv.probe，并且可以拿到設(shè)備樹里的屬性內(nèi)容。

       zsl: zsl {
              compatible = "rockchip,zslzsl";
              status = "okay";
              testdata = "test";
       };

如下修改zsl_drv_probe接口，增加拿testdata屬性的代碼

int zsl_drv_probe(struct platform_device *dev)
{
       struct property *pp = NULL;

       printk(KERN_INFO "%s: \n",__func__);

       pp = of_find_property(dev->dev.of_node, "testdata", NULL);
       if (pp)
              printk(KERN_INFO "%s: %d:%s \n",__func__,pp->length,(char *)pp->value);

       dump_stack();  // 打印堆棧

    return 0;
}

編譯運(yùn)行后如下，可以看到zsl_drv.probe會被調(diào)用到，并且能拿到設(shè)備樹里的testdata屬性。

Platform驅(qū)動和設(shè)備的關(guān)系

根據(jù)堆棧打印跟蹤代碼，調(diào)用調(diào)用關(guān)系如下

platform_driver_register
    driver_register 
        bus_add_driver   
            klist_add_tail
            driver_attach
                driver_match_device(struct device *dev, void *data)=platform_match(struct device *dev, struct device_driver *drv) //找dev
                driver_probe_device
                    really_probe
                        dev->bus->probe=platform_probe
                            drv->probe=zsl_drv_probe

Driver注冊時通過bus_add_driver將driver加入總線（klist_add_tail到總線的driver列表），觸發(fā)driver_attach，遍歷總線的device列表，通過platform_match匹配已有設(shè)備。

基本就是按順序?qū)υO(shè)備樹、id_table name的字符串匹配。匹配成功后，通過really_probe調(diào)用總線默認(rèn)的platform_probe，最終執(zhí)行driver的probe函數(shù)。

platform_device_register
    platform_device_add
        device_add
            bus_probe_device
                device_initial_probe=__device_attach
                    __device_attach_driver
                        driver_match_device(struct device *dev, void *data)=platform_match(struct device *dev, struct device_driver *drv)  //找drv
                        driver_probe_device
                            really_probe
                                dev->bus->probe=platform_probe
                                    drv->probe=zsl_drv_probe
            klist_add_tail

Device注冊時通過device_add將device加入總線（klist_add_tail到總線的device列表）觸發(fā)bus_probe_device，遍歷總線的driver列表，通過platform_match匹配已有驅(qū)動，匹配成功則調(diào)用driver的probe函數(shù)。

這種雙向注冊機(jī)制確保了無論driver和device的注冊順序如何，都能正確觸發(fā)匹配和初始化。