platform实例

1 基本模板

1.1 传统方法

在设备树出现之前, platform_device 也是需要手动去书写的.

device 代码.

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#include <linux/module.h>
#include <linux/platform_device.h>

#define DEV0_BASE_ADDR 0x10000000
#define DEV1_BASE_ADDR 0x20000000
#define RES_SIZE       0x100

/* device 0 */
static struct resource dev0_res[] = {
    [0] = {
        .start = DEV0_BASE_ADDR,
        .end   = DEV0_BASE_ADDR + RES_SIZE - 1,
        .flags = IORESOURCE_MEM,
    },
};

static void release_dev(struct device *dev) {
    pr_info(KERN_INFO "Legacy Devs: Device released\n");
}

static struct platform_device pdev0 = {
    .name = "legacy-demo-device", // core: name
    .id   = 0,                    // ID = 0
    .num_resources = ARRAY_SIZE(dev0_res),
    .resource      = dev0_res,
    .dev.release   = release_dev,
};

/* device 1 */
static struct resource dev1_res[] = {
    [0] = {
        .start = DEV1_BASE_ADDR,
        .end   = DEV1_BASE_ADDR + RES_SIZE - 1,
        .flags = IORESOURCE_MEM,
    },
};

static struct platform_device pdev1 = {
    .name = "legacy-demo-device", // core: name (must same as device 0)
    .id   = 1,                    // ID = 1
    .num_resources = ARRAY_SIZE(dev1_res),
    .resource      = dev1_res,
    .dev.release   = release_dev,
};

static int __init legacy_devs_init(void)
{
    int ret;
    pr_info(KERN_INFO "legacy devs: Registering devices...\n");
    
    platform_device_register(&pdev0);
    platform_device_register(&pdev1);
    
    return 0;
}

static void __exit legacy_devs_exit(void)
{
    platform_device_unregister(&pdev0);
    platform_device_unregister(&pdev1);
    pr_info(KERN_INFO "legacy devs: Unregistered devices.\n");
}

module_init(legacy_devs_init);
module_exit(legacy_devs_exit);
MODULE_LICENSE("GPL");

driver 代码.

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#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/io.h>

struct my_driver_data {
    int id;
    phys_addr_t phys_base;
};

static int legacy_probe(struct platform_device *pdev)
{
    struct my_driver_data *priv;
    struct resource *res;
    
    pr_info(KERN_INFO "legacy driver: Probing device ID = %d\n", pdev->id);

    priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
    if (!priv) return -ENOMEM;

    /* 1. get resources */
    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (!res) {
        dev_err(&pdev->dev, "No memory resource found\n");
        return -EINVAL;
    }

    priv->id = pdev->id;
    priv->phys_base = res->start;

    /* 3. mount private data to device */
    platform_set_drvdata(pdev, priv);

    pr_info(KERN_INFO "legacy driver: device %d initialized at 0x%llx\n", 
            priv->id, (unsigned long long)priv->phys_base);

    return 0;
}

static void legacy_remove(struct platform_device *pdev)
{
    struct my_driver_data *priv = platform_get_drvdata(pdev);
    
    pr_info(KERN_INFO "legacy driver: removing device %d (base: 0x%llx)\n", 
            priv->id, (unsigned long long)priv->phys_base);
            
}

static struct platform_driver legacy_driver = {
    .probe  = legacy_probe,
    .remove = legacy_remove,
    .driver = {
        .name = "legacy-demo-device", // core: must same as device
    },
};

module_platform_driver(legacy_driver);
MODULE_LICENSE("GPL");
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sh-5.2# insmod /lib/modules/6.18.5/updates/legacy_driver.ko 
[   18.451395] legacy_driver: loading out-of-tree module taints kernel.
sh-5.2# insmod /lib/modules/6.18.5/updates/legacy_device.ko 
[   22.298768] legacy devs: Registering devices...
[   22.299902] legacy driver: Probing device ID = 0
[   22.300307] legacy driver: device 0 initialized at 0x10000000
[   22.301217] legacy driver: Probing device ID = 1
[   22.301420] legacy driver: device 1 initialized at 0x20000000
sh-5.2# rmmod /lib/modules/6.18.5/updates/legacy_device.ko  
[   37.067971] legacy driver: removing device 0 (base: 0x10000000)
[   37.068557] Legacy Devs: Device released
[   37.068812] legacy driver: removing device 1 (base: 0x20000000)
[   37.069151] Legacy Devs: Device released
[   37.069395] legacy devs: Unregistered devices.
sh-5.2# rmmod /lib/modules/6.18.5/updates/legacy_driver.ko

1.2 设备树方法

在设备树模式下，内核优先使用 of_match_table 来寻找硬件.

  • 传统方法: 内核拿着 .name 去和设备的 .name 逐字比较.

  • 设备树: 内核优先查看 of_match_table 里的 compatible 字符串去设备树里找对应的节点.

但是它对于 /sys 来说还是非常重要.

挂挂载之后我们可以看到该文件.

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sh-5.2# ls /sys/bus/platform/drivers/dt-demo-driver/    
1000000000000100.demo  2000000000000100.demo  bind  module  uevent  unbind

内核程序.

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#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/of.h> // core
#include <linux/slab.h>

struct my_dt_data {
    phys_addr_t phys_base;
    const char *label_name;
};

static int dt_probe(struct platform_device *pdev)
{
    struct my_dt_data *priv;
    struct resource *res;
    const char *label;

    dev_info(&pdev->dev, "DT Driver: Probing started...\n");

    priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
    if (!priv) return -ENOMEM;
    /* Notice:
     * IORESOURCE_IO: for IO, need special io ins to operate it.
     * IORESOURCE_MEM: for mem space.
     * IORESOURCE_IRQ: for interrupt, now we use `platform_get_irq` replace it.
     * IORESOURCE_DMA: for DMA chanel, morden system use dmaengine replace it. 
     * ......
     */
    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (res) {
        priv->phys_base = res->start;
    }

    if (of_property_read_string(pdev->dev.of_node, "label", &label) == 0) {
        priv->label_name = label;
    } else {
        priv->label_name = "Unknown";
    }

    platform_set_drvdata(pdev, priv);

    dev_info(&pdev->dev, "DT Driver: Success! Addr=0x%llx, Label=%s\n", 
             (unsigned long long)priv->phys_base, priv->label_name);

    return 0;
}

static void dt_remove(struct platform_device *pdev)
{
    struct my_dt_data *priv = platform_get_drvdata(pdev);
    dev_info(&pdev->dev, "DT Driver: Removing %s\n", priv->label_name);
}

/* core: device match table */
static const struct of_device_id my_of_match[] = {
    { .compatible = "example,my-demo-device" },
    { /* Sentinel */ }
};
MODULE_DEVICE_TABLE(of, my_of_match);

static struct platform_driver dt_driver = {
    .probe  = dt_probe,
    .remove = dt_remove,
    .driver = {
        .name = "dt-demo-driver",
        .of_match_table = my_of_match,
    },
};

module_platform_driver(dt_driver);
MODULE_LICENSE("GPL");

运行效果.

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sh-5.2# insmod /lib/modules/6.18.5/updates/dt_driver.ko 
[  347.523308] dt-demo-driver 1000000000000100.demo: DT Driver: Probing started...
[  347.523795] dt-demo-driver 1000000000000100.demo: DT Driver: Success! Addr=0x0, Label=Instance-A
[  347.525442] dt-demo-driver 2000000000000100.demo: DT Driver: Probing started...
[  347.526605] dt-demo-driver 2000000000000100.demo: DT Driver: Success! Addr=0x0, Label=Instance-B
sh-5.2# rmmod /lib/modules/6.18.5/updates/dt_driver.ko  
[  356.249162] dt-demo-driver 2000000000000100.demo: DT Driver: Removing Instance-B
[  356.249847] dt-demo-driver 1000000000000100.demo: DT Driver: Removing Instance-A