Linux I²C Subsystem Architecture

　

Bus driver

4.1 Overview

The I²C bus driver is the software implementation of the I²C adapter, which provides the ability of the I²C adapter to complete data communication from the device, such as start, stop, response signal and master_xfer implementation function.

The I²C bus driver is described by I2c_adapter and I2c_algorithm.

Hardware description of the 4.2 S3C2440I2C controller

The s3c2440 processor incorporates an I²C controller with four registers for control:

Iiccon i²c Control Register

Iicstat i²c Status Register

Iicds I²C Transceiver Data Shift Register

Iicadd i²c Address Register

With the Iiccon,iicds,iicadd register operation, the start bit, stop bit, data and address are generated on the I²c bus, while the transmitted state is obtained through the Iicstat register.

4.3 i2c-s3c2410 bus driver analysis (platform_driver)

I²c bus driver code in DRIVERS/I2C/BUSSES/I2C-S3C2410.C, this code also supports the S3C2410,S3C6410,S5PC110 and other Samsung series of chips.

Initializing modules and unloading modules

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1. static int __init i2c_adap_s3c_init (void)
2. {
3. Returnplatform_driver_register (&s3c24xx_i2c_driver);
4. }
6. static void __exit i2c_adap_s3c_exit (void)
7. {
8. Platform_driver_unregister (&s3c24xx_i2c_driver);
9. }

Bus driver is based on platform, which conforms to the idea of device-driven model.

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2. static struct Platform_drivers3c24xx_i2c_driver = {
4. . Probe = S3c24xx_i2c_probe,
6. . remove = S3c24xx_i2c_remove,
8. . id_table = S3c24xx_driver_ids,
10. . Driver = {
12. . Owner = This_module,
14. . Name = "S3C-I2C",
16. . PM = S3c24xx_dev_pm_ops,
18. . of_match_table= S3c24xx_i2c_match,
20. },
22. };

S3c24xx_i2c_probe function

When the Platform_driver_register function is called to register the platform_driver struct, if Platformdevice and platform driver match successfully, the probe function is called to initialize the adapter hardware.

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2. static int S3c24xx_i2c_probe (structplatform_device *pdev)
4. {
6. ......
8. / * Initialize Adapter information * /
10. strlcpy (I2c->adap.name,"S3C2410-I2C", sizeof (i2c->adap.name));
12. I2c->adap.owner = This_module;
14. I2c->adap.algo = &s3c24xx_i2c_algorithm;
16. I2c->adap.retries= 2;
18. I2c->adap. class = I2c_class_hwmon |  I2C_CLASS_SPD;
20. I2c->tx_setup = 50;
24. /* Initialize spin lock and wait queue header */
26. Spin_lock_init (&i2c->lock);
28. Init_waitqueue_head (&i2c->wait);
32. / * Map Register * /
34. Res= Platform_get_resource (Pdev, Ioresource_mem, 0);
36. I2c->ioarea= request_mem_region (Res->start, Resource_size (res),
38. Pdev->name);
40. I2c->regs= Ioremap (Res->start, Resource_size (res));
44. / * Set the information required for the I²C core * /
46. I2c->adap.algo_data= I²c;
48. I2c->adap.dev.parent= &pdev->dev;
52. / * Initialize the I²C controller * /
54. ret= S3c24xx_i2c_init (I²C);
58. / * Request interrupted * /
60. i2c->irq= ret = PLATFORM_GET_IRQ (pdev, 0);
62. Ret= Request_irq (I2C->IRQ, S3C24XX_I2C_IRQ, 0,
64. Dev_name (&pdev->dev), i²c);
68. / * Register the I²C adapter * /
70. ret= I2c_add_numbered_adapter (&I2C->ADAP);
72. ......
74. }

Probe main work is when the hardware and request the I²C adapter to use the IO address, interrupt number, etc., and then add this adapter to the I²c core. I2c_adapter Registration Process I2c_add_numbered_adapter->i2c_register_adapter

I²c Bus Communication method

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1. static const struct i2c_algorithms3c24xx_i2c_algorithm = {
2. . Master_xfer = S3c24xx_i2c_xfer,
3. . functionality = S3c24xx_i2c_func,
4. };

S3c24xx_i2c_xfer function is the realization of bus communication mode, which relies on two functions of S3c24xx_i2c_doxfer and S3c24xx_i2c_message_start;

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2. static int S3c24xx_i2c_doxfer (STRUCTS3C24XX_I2C *i2c,
4. struct i2c_msg *msgs, int num)
6. {
8. RET =s3c24xx_i2c_set_master (I²C);
12. I2c->msg = msgs;
14. i2c->msg_num= num;
16. I2c->msg_ptr= 0;
18. i2c->msg_idx= 0;
20. I2c->state = State_start;
24. S3c24xx_i2c_message_start (I2C,MSGS);
26. }

First set the S3C i²c device as the primary device, and then call the S3c24xx_i2c_message_start function to start the I²C message transfer.

The S3c24xx_i2c_func function returns the communication capabilities supported by the adapter.

4.4 Device Resources for adapters (Platform_device)

S3C2440 's I²c bus driver is based on the platform to achieve, we analyzed the Platformdriver section, and then look at the platform device part.

The resource information for the Platform_device struct and the I²C controller is defined in the arch/arm/plat-samsung/dev-i2c0.c file:

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2. Static struct resource s3c_i2c_resource[] ={
4. [0]= {
6. . start= S3C_PA_IIC,
8. . end = S3c_pa_iic + Sz_4k-1,
10. . flags= Ioresource_mem,
12. },
14. [1]= {
16. . start= IRQ_IIC,
18. . end = IRQ_IIC,
20. . flags= Ioresource_irq,
22. },
24. };
28. struct Platform_device s3c_device_i2c0 = {
30. . Name = "S3C2410-I2C",/ * Device name * /
32. #ifdef CONFIG_S3C_DEV_I2C1
34. . id = 0,
36. #else
38. . id =-1,
40. #endif
42. . Num_resources =array_size (S3c_i2c_resource),
44. . Resource =s3c_i2c_resource,
46. };
50. struct S3c2410_platform_i2cdefault_i2c_data __initdata = {
52. . Flags = 0,
54. . slave_addr = 0x10,/ */i²c Adapter Address * /
56. . frequency = 100*1000,/ * Bus frequency * /
58. . Sda_delay = +,/ * SDA Edge delay Time NS * /
60. };
64. void __init S3c_i2c0_set_platdata (structs3c2410_platform_i2c *pd)
66. {
68. STRUCTS3C2410_PLATFORM_I2C *NPD;
72. if (!PD)
74. Pd= &default_i2c_data;
78. Npd= S3c_set_platdata (PD, sizeof (struct S3C2410_PLATFORM_I2C),
80. &S3C_DEVICE_I2C0);
84. if (!npd->cfg_gpio)
86. Npd->cfg_gpio= S3c_i2c0_cfg_gpio;
88. }

Register the Platform_device into the kernel in the board file:

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1. Static struct platform_device*mini2440_devices[] __initdata = {
2. ......
3. &S3C_DEVICE_I2C0,
4. ......
5. };

Call the S3c_i2c0_set_platdata function to assign the adapter specific data to Dev.platform_data:

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1. static void __init mini2440_init (void)
2. {
3. ......
4. S3c_i2c0_set_platdata (NULL);
5. }

The I²c bus driver is analyzed here.

Linux I²C Subsystem Architecture