Linux pinctrl子系统介绍

在很多SOC内部都有pin的控制器，通过配置pin控制器，可以将引脚配置为特定的功能特性，在软件方面，linux内核提供pinctrl子系统，目的为了统一soc厂商的pin脚管理。

以NXP i.MX7D为例，每个IO引脚有多达8种的复用功能，具体用哪一种功能，通过IOMUXC来配置引脚的具体特性。

Linux pinctrl的处理工作

引脚复用

在Linux内核DT文件夹中arch/arm/boot/dts/imx7d-pinfunc.h的文件中，定义了所有引脚的复用配置。以下面的为例

#define MX7D_PAD_I2C1_SDA_GPIO4_IO9   0x014c 0x03BC 0x0000 0x5 0x0

• 0x014c是IOMUXC_SW_MUX_CTL_PAD_I2C1_SDA多路复用寄存器的偏移量

• 0x03BC是IOMUXC_SW_PAD_CTL_PAD_I2C1_SDA控制寄存器的偏移量

• 0x5 是IOMUXC_SW_MUX_CTL_PAD_I2C1_SDA多路复用寄存器ALT5的模式，也就当做普通的GPIO来用

引脚配置

引脚的具体配置，从linux3.x内核后都是在设备树中进行具体的复用和配置。

以ledclassRGB节点为例,此节点对应的IO配置为pinctrl_gpio_leds、pinctrl_gpio_led，其中pinctrl_gpio_leds主要对MX7D_PAD_SAI2_TX_BCLK__GPIO6_IO20、MX7D_PAD_SAI2_RX_DATA__GPIO6_IO21引脚进行复用，最后的0x11是配置前面控制寄存器的值

0x11

mux_reg：复用配置寄存器偏移地址
conf_reg：引脚配置寄存器偏移地址
input_reg：输入配置寄存器偏移地址
mux_mode：复用配置寄存器值
input_val：输入配置寄存器值

ledclassRGB {compatible = "arrow,RGBclassleds";reg = <0x30200000 0x60000>;    pinctrl-names = "default";pinctrl-0 = <&pinctrl_gpio_leds &pinctrl_gpio_led>;red {label = "red";};green {label = "green";};blue {label = "blue";linux,default-trigger = "heartbeat";};};pinctrl_gpio_leds: pinctrl_gpio_leds_grp {fsl,pins = ;};

MMIO(内存映射IO)设备访问

对外围设备的控制是通过写入及读取其寄存器来实现的，通过内存地址空间（MMIO）或地址空间（PIO）的连续地址来访问这些寄存器的

1：MMIO

主存和IO设备使用相同的总线地址

使用常规指令访问IO设备

linux支持的不同体系结构中使用广泛的IO方法

2：PIO

主存和IO设备使用不同的地址空间

使用特殊的CPU指令来访问IO设备

x86上的示例：IN和OUT指令

i.MX7D使用的是MMIO，但是驱动程序中无法直接访问物理地址，需要MMU进行映射。

可以通过下面的函数

1：使用ioremap、iounmap

2: 使用devm_ioremap、devm_iounmap

3：ioread8\ioread16 iowrite8\iowrite16

LED驱动示例：

#include 
#include 
#include 
#include 
#include 
#include #define GPDAT1_offset        0x00
#define GPDIR1_offset        0x04
#define GPDAT6_offset        0x50000
#define GPDIR6_offset        0x50004#define GPIO1_DIR_MASK 1 << 2
#define GPIO1_DATA_MASK 1 << 2#define GPIO6_DIR_MASK (1 << 20 | 1 << 21)
#define GPIO6_DATA_MASK (1 << 20 | 1 << 21)#define LED_RED_MASK 1 << 2
#define LED_GREEN_MASK 1 << 20
#define LED_BLUE_MASK 1 << 21struct led_dev
{u32 led_mask; /* different mask if led is R,G or B */void __iomem *base;struct led_classdev cdev;
};static void led_control(struct led_classdev *led_cdev, enum led_brightness b)
{u32 read, write;struct led_dev *led = container_of(led_cdev, struct led_dev, cdev);if (b != LED_OFF) { /* LED ON */if (led->led_mask == LED_RED_MASK) {read = ioread32(led->base + GPDAT1_offset);write = read | led->led_mask;iowrite32(write, led->base + GPDAT1_offset);}if ((led->led_mask == LED_GREEN_MASK) || (led->led_mask == LED_BLUE_MASK)) {read = ioread32(led->base + GPDAT6_offset);write = read | led->led_mask;iowrite32(write, led->base + GPDAT6_offset);}}else {if (led->led_mask == LED_RED_MASK) {read = ioread32(led->base + GPDAT1_offset);write = read & ~(led->led_mask);iowrite32(write, led->base + GPDAT1_offset);}if ((led->led_mask == LED_GREEN_MASK) || (led->led_mask == LED_BLUE_MASK)) {read = ioread32(led->base + GPDAT6_offset);write = read & ~(led->led_mask);iowrite32(write, led->base + GPDAT6_offset);}}
}static int __init ledclass_probe(struct platform_device *pdev)
{u32 GPDIR1_read, GPDIR1_write;u32 GPDIR6_read, GPDIR6_write;u32 GPDAT1_read, GPDAT1_write;u32 GPDAT6_read, GPDAT6_write;void __iomem *g_ioremap_addr;struct device_node *child;struct resource *r;struct device *dev = &pdev->dev;int count, ret;dev_info(dev, "platform_probe enter\n");/* get our first memory resource from device tree */r = platform_get_resource(pdev, IORESOURCE_MEM, 0);if (!r) {dev_err(dev, "IORESOURCE_MEM, 0 does not exist\n");return -EINVAL;}dev_info(dev, "r->start = 0x%08lx\n", (long unsigned int)r->start);dev_info(dev, "r->end = 0x%08lx\n", (long unsigned int)r->end);/* ioremap our memory region */g_ioremap_addr = devm_ioremap(dev, r->start, resource_size(r));if (!g_ioremap_addr) {dev_err(dev, "ioremap failed \n");return -ENOMEM;}count = of_get_child_count(dev->of_node);if (!count)return -EINVAL;dev_info(dev, "there are %d nodes\n", count);/* Set GPIO1_IO_2 direction bit to output */GPDIR1_read = ioread32(g_ioremap_addr + GPDIR1_offset);GPDIR1_write = GPDIR1_read | (GPIO1_DIR_MASK);iowrite32(GPDIR1_write, g_ioremap_addr + GPDIR1_offset);GPDIR6_read = ioread32(g_ioremap_addr + GPDIR6_offset);GPDIR6_write = GPDIR6_read | (GPIO6_DIR_MASK);iowrite32(GPDIR6_write, g_ioremap_addr + GPDIR6_offset);/* set all leds to 0 output */GPDAT1_read = ioread32(g_ioremap_addr + GPDAT1_offset);GPDAT1_write = GPDAT1_read & ~(GPIO1_DATA_MASK);iowrite32(GPDAT1_write, g_ioremap_addr + GPDAT1_offset);GPDAT6_read = ioread32(g_ioremap_addr + GPDAT6_offset);GPDAT6_write = GPDAT6_read & ~(GPIO6_DATA_MASK);iowrite32(GPDAT6_write, g_ioremap_addr + GPDAT6_offset);for_each_child_of_node(dev->of_node, child){struct led_dev *led_device;struct led_classdev *cdev;led_device = devm_kzalloc(dev, sizeof(*led_device), GFP_KERNEL);if (!led_device)return -ENOMEM;cdev = &led_device->cdev;led_device->base = g_ioremap_addr;of_property_read_string(child, "label", &cdev->name);if (strcmp(cdev->name,"red") == 0) {led_device->led_mask = LED_RED_MASK;led_device->cdev.default_trigger = "heartbeat";}else if (strcmp(cdev->name,"green") == 0) {led_device->led_mask = LED_GREEN_MASK;}else if (strcmp(cdev->name,"blue") == 0) {led_device->led_mask = LED_BLUE_MASK;}else {dev_info(dev, "Bad device tree value\n");return -EINVAL;}/* Disable timer trigger until led is on */led_device->cdev.brightness = LED_OFF;led_device->cdev.brightness_set = led_control;ret = devm_led_classdev_register(dev, &led_device->cdev);if (ret) {dev_err(dev, "failed to register the led %s\n", cdev->name);of_node_put(child);return ret;}}dev_info(dev, "leds_probe exit\n");return 0;
}static int __exit ledclass_remove(struct platform_device *pdev)
{dev_info(&pdev->dev, "leds_remove enter\n");dev_info(&pdev->dev, "leds_remove exit\n");return 0;
}static const struct of_device_id my_of_ids[] = {{ .compatible = "arrow,RGBclassleds"},{},
};MODULE_DEVICE_TABLE(of, my_of_ids);static struct platform_driver led_platform_driver = {.probe = ledclass_probe,.remove = ledclass_remove,.driver = {.name = "RGBclassleds",.of_match_table = my_of_ids,.owner = THIS_MODULE,}
};static int ledRGBclass_init(void)
{int ret_val;pr_info("demo_init enter\n");ret_val = platform_driver_register(&led_platform_driver);if (ret_val !=0){pr_err("platform value returned %d\n", ret_val);return ret_val;}pr_info("demo_init exit\n");return 0;
}static void ledRGBclass_exit(void)
{pr_info("led driver enter\n");platform_driver_unregister(&led_platform_driver);pr_info("led driver exit\n");
}module_init(ledRGBclass_init);
module_exit(ledRGBclass_exit);MODULE_LICENSE("GPL");
MODULE_AUTHOR("Alberto Liberal ");
MODULE_DESCRIPTION("This is a driver that turns on/off RGB leds \using the LED subsystem");