5. GPIO¶
5.1. Introduction¶
GPIO (General-Purpose Input/Output) is a General pin that can be dynamically configured and controlled during software operation.The initial state of all GPIOs after power-on is input mode, which can be set as pull-up or pull-down or interrupt pin by software. The driving intensity is programmable, and the core of which is to fill the methods and parameters of GPIO bank and register them in the kernel by calling gpiochip_add.
5.2. GPIO Pin to calculate¶
C40PL have 5 GPIO bank：GPIO0~GPIO4，Each group was numbered A0~A7, B0~B7, C0~C7, and D0~D7, the following formulas are often used to calculate GPIO Pin:
GPIO pin calculation formula：pin = bank * 32 + number
GPIO group number calculation formula：number = group * 8 + X
#define RK_PA0 0
#define RK_PA1 1
#define RK_PA2 2
#define RK_PA3 3
#define RK_PA4 4
#define RK_PA5 5
#define RK_PA6 6
#define RK_PA7 7
#define RK_PB0 8
#define RK_PB1 9
#define RK_PB2 10
#define RK_PB3 11
......
When the GPIO2_C0 pin is not reused by other peripherals, we can export the pin to use it.
[root@RV1126_RV1109:/]# ls /sys/class/gpio/
export gpiochip0 gpiochip128 gpiochip32 gpiochip503 gpiochip511 gpiochip64 gpiochip96 unexport
[root@RV1126_RV1109:/]# echo 80 > /sys/class/gpio/export
[root@RV1126_RV1109:/]# ls /sys/class/gpio/
export gpio80 gpiochip0 gpiochip128 gpiochip32 gpiochip503 gpiochip511 gpiochip64 gpiochip96 unexport
[root@RV1126_RV1109:/]# ls /sys/class/gpio/gpio80
active_low device direction edge power subsystem uevent value
5.3. Input And Output¶
5.3.1. Application Layer Settings¶
After exporting the pins above, you can directly set the gpio to input mode or output mode
View the current gpio mode
[root@RV1126_RV1109:/]# cat /sys/class/gpio/gpio80/direction
in
Set to input mode
[root@RV1126_RV1109:/]# echo in > /sys/class/gpio/gpio80/direction
In input mode, directly view the value of the value file to know the input level
[root@RV1126_RV1109:/]# cat /sys/class/gpio/gpio80/value
0
Set to output mode
[root@RV1126_RV1109:/]# echo out > /sys/class/gpio/gpio80/direction
设置输出高电平
[root@RV1126_RV1109:/]# echo 1 > /sys/class/gpio/gpio80/value
Set output high level
[root@RV1126_RV1109:/]# echo 0 > /sys/class/gpio/gpio80/value
5.3.2. Driver Layer Settings¶
of_get_named_gpio_flags reads the GPIO configuration numbers and flags of firefly-gpio and firefly-irq-gpio from the device tree, gpio_is_valid judges whether the GPIO number is valid, and gpio_request applies to occupy the GPIO. If there is an error in the initialization process, you need to call gpio_free to release the previously applied and successful GPIO. Call gpio_direction_output in the driver to set the output high or low level. Here the default output is the active level GPIO_ACTIVE_HIGH obtained from DTS, which is high level. If the drive works normally, you can use a multimeter to measure the corresponding The pin should be high. In practice, if you want to read GPIO, you need to set it to input mode first, and then read the value:
int val;
gpio_direction_input(your_gpio);
val = gpio_get_value(your_gpio);
The following are commonly used GPIO API definitions:
#include <linux/gpio.h>
#include <linux/of_gpio.h>
enum of_gpio_flags {
OF_GPIO_ACTIVE_LOW = 0x1,
};
int of_get_named_gpio_flags(struct device_node *np, const char *propname,
int index, enum of_gpio_flags *flags);
int gpio_is_valid(int gpio);
int gpio_request(unsigned gpio, const char *label);
void gpio_free(unsigned gpio);
int gpio_direction_input(int gpio);
int gpio_direction_output(int gpio, int v);
5.4. Interrupt¶
IRQ_TYPE_EDGE_RISING indicates that the interrupt is triggered by the rising edge, and the interrupt function can be triggered when the pin receives the rising edge signal.This can also be configured as follows：
IRQ_TYPE_NONE //Default value, no defined interrupt trigger type
IRQ_TYPE_EDGE_RISING //Rising edge trigger
IRQ_TYPE_EDGE_FALLING //Falling edge trigger
IRQ_TYPE_EDGE_BOTH //Trigger on both rising and falling edges
IRQ_TYPE_LEVEL_HIGH //High level trigger
IRQ_TYPE_LEVEL_LOW //Low level trigger
Then analyze the resources added by DTS in the probe function, and then apply for interrupted registration, the code is as follows:
static int firefly_gpio_probe(struct platform_device *pdev)
{
int ret;
int gpio;
enum of_gpio_flags flag;
struct firefly_gpio_info *gpio_info;
struct device_node *firefly_gpio_node = pdev->dev.of_node;
...
gpio_info->firefly_irq_gpio = gpio;
gpio_info->firefly_irq_mode = flag;
gpio_info->firefly_irq = gpio_to_irq(gpio_info->firefly_irq_gpio);
if (gpio_info->firefly_irq)
{
if (gpio_request(gpio, "firefly-irq-gpio"))
{
dev_err(&pdev->dev, "firefly-irq-gpio: %d request failed!\n", gpio);
gpio_free(gpio);
return IRQ_NONE;
}
ret = request_irq(gpio_info->firefly_irq, firefly_gpio_irq,
flag, "firefly-gpio", gpio_info);
if (ret != 0)
{
free_irq(gpio_info->firefly_irq, gpio_info);
dev_err(&pdev->dev, "Failed to request IRQ: %d\n", ret);
}
}
printk("Firefly irq gpio finish \n");
return 0;
}
static irqreturn_t firefly_gpio_irq(int irq, void *dev_id) //interrupt function
{
printk("Enter firefly gpio irq test program!\n");
return IRQ_HANDLED;
}
Call gpio_to_irq to convert the PIN value of the GPIO to the corresponding IRQ value, call gpio_request to apply for the IO port, call request_irq to apply for an interrupt, if it fails, call free_irq to release, in this function gpio_info-firefly_irq Is the hardware interrupt number to be applied for, firefly_gpio_irq is the interrupt function, gpio_info->firefly_irq_mode is the attribute of interrupt processing, firefly-gpio is the name of the device driver, and gpio_info is the device structure of the device. It is used when registering shared interrupts.
5.5. Reuse¶
For reference only, the actual hardware interfaces prevail.
In addition to general input and output and interrupt functions, GPIO ports may also have other multiplexing functions. Taking GPIO0_C3 as an example, there are several functions as follows:
| func0 | func1 | func2 |
|---|---|---|
| GPIO0_C3 | I2C2_SDA | PWM5_M0 |
Check /sys/kernel/debug/pinctrl/pinctrl-rockchip-pinctrl/pinmux-pins to check the functions of each pin. If you find that GPIO0_C2 and GPIO0_C3 are multiplexed as I2C, you need to turn it off in dts
&i2c2 {
status = "disabled";
};
Note: Here GPIO0_C2 is only used as an example. It is not recommended to modify it in actual use
The above introduces the modification on DTS, so how to switch functions at runtime? The following is a brief introduction using I2C2 as an example. For detailed introduction, please refer to docs/Common/Pin-Ctrl/Rockchip-Developer-Guide-Linux-Pin-Ctrl-CN.pdf.
According to the specification table, the function definitions of I2C2_SDA and I2C2_SCL are as follows:
| Pad# | func0 | func1 | func2 |
|---|---|---|---|
| PWM4_M0 | GPIO0_C2 | I2C2_SCL | PWM4_M0 |
| PWM5_M0 | GPIO0_C3 | I2C2_SDA | PWM4_M0 |
In kernel/arch/arm/boot/dts/rv1126.dtsi:
i2c2: i2c@ff400000 {
compatible = "rockchip,rv1126-i2c", "rockchip,rk3399-i2c";
reg = <0xff400000 0x1000>;
interrupts = <GIC_SPI 6 IRQ_TYPE_LEVEL_HIGH>;
#address-cells = <1>;
#size-cells = <0>;
rockchip,grf = <&pmugrf>;
clocks = <&pmucru CLK_I2C2>, <&pmucru PCLK_I2C2>;
clock-names = "i2c", "pclk";
pinctrl-names = "default";
pinctrl-0 = <&i2c2_xfer>;
status = "disabled";
};
The attributes starting with pinctrl- are related to multiplexing control:
pinctrl-names defines a list of state names: default (i2c function) and gpio.
pinctrl-0 defines the pinctrl that needs to be set when state 0 (i.e. default): &i2c2_xfer
pinctrl-1 defines the pinctrl that needs to be set when state 1 (i.e. gpio): &i2c2_gpio
These pinctrls are defined in kernel/arch/arm/boot/dts/rv1126.dtsi as follows:
pinctrl: pinctrl {
compatible = "rockchip,rv1126-pinctrl";
rockchip,grf = <&grf>;
rockchip,pmu = <&pmugrf>;
#address-cells = <1>;
#size-cells = <1>;
ranges;
...
};
In kernel/arch/arm/boot/dts/rv1126.dtsi, there is the definition of i2c2
i2c2 {
/omit-if-no-ref/
i2c2_xfer: i2c2-xfer {
rockchip,pins =
/* i2c2_scl */
<0 RK_PC2 1 &pcfg_pull_none_drv_level_0_smt>,
/* i2c2_sda */
<0 RK_PC3 1 &pcfg_pull_none_drv_level_0_smt>;
};
};
RK_FUNC_GPIO is defined in kernel/include/dt-bindings/pinctrl/rockchip.h, here it is abbreviated as 0:
#define RK_FUNC_GPIO 0
After knowing the above definition of i2c2, in the kernel’s dts Add gpio resources for i2c2 nodes in the file
&i2c2 {
status = "okay";
pinctrl-names = "default","i2c2_gpio";
pinctrl-1 = <&i2c2_gpio>;
gpios = <&gpio0 RK_PC2 GPIO_ACTIVE_HIGH>,<&gpio0 RK_PC3 GPIO_ACTIVE_HIGH>;
};
&pinctrl {
i2c2{
/omit-if-no-ref/
i2c2_gpio: i2c2-gpio{
rockchip,pins =
/* i2c2_gpio0_c2 */
<0 RK_PC2 0 &pcfg_pull_none>,
/* i2c2_gpio0_c3 */
<0 RK_PC3 0 &pcfg_pull_none>;
};
};
};
The I2C driver registration process is as follows:
rk3x_i2c_driver_init
platform_driver_register
driver_register
bus_add_driver
driver_attach
bus_for_each_dev
__driver_attach
device_driver_attach
driver_probe_device
really_probe
pinctrl_bind_pins
pinctrl_select_state
pinctrl_select_state is a function to select pinctrl in dts.
5.6. Debugging Method¶
5.6.1. IO Instruction¶
A very useful tool for GPIO debugging is the IO command. The Android system of C40PL has built-in IO commands by default. Using IO commands, you can read or write the status of each IO port in real time. Here is a brief introduction The use of IO instructions. First check the help of IO instruction:
[root@RV1126_RV1109:/]# io --help
Unknown option: ?
Raw memory i/o utility - $Revision: 1.5 $
io -v -1|2|4 -r|w [-l <len>] [-f <file>] <addr> [<value>]
-v Verbose, asks for confirmation
-1|2|4 Sets memory access size in bytes (default byte)
-l <len> Length in bytes of area to access (defaults to
one access, or whole file length)
-r|w Read from or Write to memory (default read)
-f <file> File to write on memory read, or
to read on memory write
<addr> The memory address to access
<val> The value to write (implies -w)
Examples:
io 0x1000 Reads one byte from 0x1000
io 0x1000 0x12 Writes 0x12 to location 0x1000
io -2 -l 8 0x1000 Reads 8 words from 0x1000
io -r -f dmp -l 100 200 Reads 100 bytes from addr 200 to file
io -w -f img 0x10000 Writes the whole of file to memory
Note access size (-1|2|4) does not apply to file based accesses.
As you can see from the help, if you want to read or write a register, you can use:
io -4 -r 0x1000 //Read the value of 4-bit register starting from 0x1000
io -4 -w 0x1000 //Write the value of the 4-bit register from 0x1000
Usage example:
Check the multiplexing of GPIO0_C2 pin
From the datasheet of the master controller, the base address of the register corresponding to GPIO0 is: 0xFE020000
From the datasheet of the master controller, the offset of GPIO0D_IOMUX is: 0x0010
The iomux register address of GPIO0_C2 is: base address (Operational Base) + offset (offset) = 0xFE020000 + 0x0010 = 0xFE020010
Use the following command to check the multiplexing of GPIO1_D0:
[root@RV1126_RV1109:/]# io -4 -r 0xFE020010
fe020010: 00000020
From the trm datasheet [10:8]:
gpio0c2_sel
3'h0: GPIO0_C2_d
3'h1: I2C2_SCL
3'h3: PWM4_PIN_M0
Others: Reserved
Therefore, it can be determined that the GPIO is multiplexed as GPIO0_C2_d.
If you want to multiplex as I2C2_SCL, you can use the following command to set:
[root@RV1126_RV1109:/]# io -4 -w 0xFE020010 0x1000120
5.6.2. GPIO Debug Interface¶
The purpose of the Debugfs file system is to provide developers with more kernel data to facilitate debugging. Here GPIO debugging can also use the Debugfs file system to get more kernel information. The interface of GPIO in the Debugfs file system is /sys/kernel/debug/gpio, the information of this interface can be read like this:
[root@RV1126_RV1109:/]# cat /sys/kernel/debug/gpio
gpiochip0: GPIOs 0-31, parent: platform/pinctrl, gpio0:
gpio-2 ( |gpio_fan ) out hi
gpio-4 ( |firefly:blue:power ) out lo
gpio-5 ( |bt_default_wake_host) in hi
gpio-6 ( |reset ) out hi
gpio-7 ( |bt_default_poweron ) out hi
gpio-16 ( |firefly:yellow:user ) out lo
gpio-28 ( |GTP rst gpio ) in hi
gpio-30 ( |enable ) out hi
gpiochip1: GPIOs 32-63, parent: platform/pinctrl, gpio1:
gpio-32 ( |GTP int gpio ) in lo
gpio-34 ( |reset ) out hi
gpio-35 ( |enable ) out hi
gpio-48 ( |bt_default_rts ) out lo
gpio-52 ( |vcc5v0_usb2_host ) out hi
gpio-53 ( |hp-det-gpio ) in lo
gpio-54 ( |vcc_otg_vbus ) out hi
gpio-55 ( |hp-ctl ) out lo
gpio-60 ( |pwdn ) out lo
gpiochip2: GPIOs 64-95, parent: platform/pinctrl, gpio2:
gpio-69 ( |vcc_4g ) out hi
gpio-74 ( |mdio-reset ) out hi
...
From the information read, we can know that the kernel lists the current status of GPIO. Taking the GPIO1 group as an example, gpio-55 (GPIO1_C7) outputs a low level (out lo).
5.6.3. pinmux-pins¶
Command:
[root@RV1126_RV1109:/]# cat /sys/kernel/debug/pinctrl/pinctrl-rockchip-pinctrl/pinmux-pins
Result:
Pinmux settings per pin
Format: pin (name): mux_owner gpio_owner hog?
pin 0 (gpio0-0): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 1 (gpio0-1): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 2 (gpio0-2): gpio-fan gpio0:2 function gpio_fan group fan-pins
pin 3 (gpio0-3): ffc60000.dwmmc (GPIO UNCLAIMED) function sdmmc0 group sdmmc0-det
pin 4 (gpio0-4): (MUX UNCLAIMED) gpio0:4
pin 5 (gpio0-5): (MUX UNCLAIMED) gpio0:5
pin 6 (gpio0-6): sdio-pwrseq gpio0:6 function sdio-pwrseq group wifi-enable-h
...
Analysis:
The column pin 0 indicates the pin number, the column gpio0-0 indicates the gpio group number, the column MUX UNCLAIMED indicates the owner of the data selector, and the column GPIO UNCLAIMED indicates the owner of the gpio.
Among them, MUX UNCLAIMED indicates that the pin has not been controlled by the node using pinctrl. GPIO UNCLAIMED indicates that no registered gpio uses the pin.
5.7. FAQs¶
5.7.1. Q1: How to switch the MUX value of PIN to normal GPIO?¶
A1: When using GPIO request, the MUX value of the PIN will be forcibly switched to GPIO, so when using the PIN pin as a GPIO function, make sure that the PIN pin is not used by other modules.
5.7.2. Q2: Why is the value I read out with the IO instruction is 0x00000000?¶
A2: If you use the IO command to read the register of a GPIO, the value read is abnormal, such as 0x00000000 or 0xffffffff, etc., please confirm whether the CLK of the GPIO is turned off. The CLK of the GPIO is controlled by the CRU. You can read the datasheet Next, use the CRU_CLKGATE_CON* register to check whether the CLK is turned on. If it is not turned on, you can use the io command to set the corresponding register to turn on the corresponding CLK. After turning on the CLK, you should be able to read the correct register value.
5.7.3. Q3: How to check if the voltage of the PIN pin is wrong?¶
A3: When measuring the voltage of the PIN pin is incorrect, if external factors are excluded, you can confirm whether the IO voltage source where the PIN is located is correct and whether the IO-Domain configuration is correct.
5.7.4. Q4: What is the difference between gpio_set_value() and gpio_direction_output()?¶
A4: If you do not dynamically switch input and output when using this GPIO, it is recommended to set the GPIO output direction at the beginning, and use the gpio_set_value() interface when pulling it up and pulling it down later. It is not recommended to use gpio_direction_output() because of the gpio_direction_output interface There is a mutex lock inside, there will be an error exception when calling the interrupt context, and compared to gpio_set_value, gpio_direction_output does more and is wasteful.