作者信息
作者: 彭東林
QQ：405728433
平臺簡介
開發板：tiny4412ADK + S700 + 4GB Flash
要移植的內核版本：Linux-4.4.0 （支持device tree）
u-boot版本：友善之臂自帶的 U-Boot 2010.12 （為支持uImage啟動，做了少許改動）
busybox版本：busybox 1.25
交叉編譯工具鏈： arm-none-linux-gnueabi-gcc
（gcc version 4.8.3 20140320 (prerelease) (Sourcery CodeBench Lite 2014.05-29)）
摘要
MMA7660是一個三軸加速度感測器，跟exynos4412之間使用I2C介面進行通信，同時MMA7660可以向exynos4412發起外部中斷。
移植MMA7660驅動會涉及到device tree、I2C驅動、中斷、輸入子系統等幾個部分，tiny4412自帶的MMA7660驅動程式是不支持設備樹的，同時I2C驅動也沒有採用設備樹，所以主要的工作量就是將MMA7660和I2C驅動程式從非設備樹形式轉變為設備樹的形式。同時藉此機會，學習一下有設備樹的情況下的設備驅動（MMA7660和I2C）和中斷。
移植
一、原理圖
下麵是MMA7660的在底板原理圖：
可以看到，使用的是第3個I2C控制器。
下麵是核心板：
I2C：
XEINT25：
二、tiny4412自帶的驅動
tiny4412自帶的mma7660驅動並不是採用設備樹，但是可以作為我們的參考，在arch/arm/mach-exynos/mach-tiny4412.c中包含了mma7660的板級信息。
MMA7660的板級信息：
1: #include <linux/mma7660.h>
2: static struct mma7660_platform_data mma7660_pdata = {
3: .irq = IRQ_EINT(25),
4: .poll_interval = 100,
5: .input_fuzz = 4,
6: .input_flat = 4,
7: };
8:
9: static struct s3c2410_platform_i2c tiny4412_i2c3_data __initdata = {
10: .flags = 0,
11: .bus_num = 3,
12: .slave_addr = 0x10,
13: .frequency = 200*1000,
14: .sda_delay = 100,
15: };
16:
17: static struct i2c_board_info i2c_devs3[] __initdata = {
18: {
19: I2C_BOARD_INFO("mma7660", 0x4c),
20: .platform_data = &mma7660_pdata,
21: },
22: };
23:
24: static void __init smdk4x12_machine_init(void)
25: {
26: ... ...
27: s3c_i2c3_set_platdata(&tiny4412_i2c3_data);
28: i2c_register_board_info(3, i2c_devs3, ARRAY_SIZE(i2c_devs3)); // 註冊板級信息
29: ... ...
30: }
其中，
從上面的信息我們可以知道：
MMA7660的器件地址是0x4c，I2C3的CLK信號新的頻率為200KHz。這兩個信息比較重要。MMA7660的驅動程式是linux-3.0.86/drivers/hwmon/mma7660.c。
I2C的板級信息：
在arch/arm/plat-samsung/dev-i2c3.c中：
1: /* linux/arch/arm/plat-samsung/dev-i2c3.c
2: *
3: * Copyright (c) 2010 Samsung Electronics Co., Ltd.
4: * http://www.samsung.com/
5: *
6: * S5P series device definition for i2c device 3
7: *
8: * This program is free software; you can redistribute it and/or modify
9: * it under the terms of the GNU General Public License version 2 as
10: * published by the Free Software Foundation.
11: */
12:
13: #include <linux/gfp.h>
14: #include <linux/kernel.h>
15: #include <linux/string.h>
16: #include <linux/platform_device.h>
17:
18: #include <mach/irqs.h>
19: #include <mach/map.h>
20:
21: #include <plat/regs-iic.h>
22: #include <plat/iic.h>
23: #include <plat/devs.h>
24: #include <plat/cpu.h>
25:
26: static struct resource s3c_i2c_resource[] = {
27: [0] = {
28: .start = S3C_PA_IIC3,
29: .end = S3C_PA_IIC3 + SZ_4K - 1,
30: .flags = IORESOURCE_MEM,
31: },
32: [1] = {
33: .start = IRQ_IIC3,
34: .end = IRQ_IIC3,
35: .flags = IORESOURCE_IRQ,
36: },
37: };
38:
39: struct platform_device s3c_device_i2c3 = {
40: .name = "s3c2440-i2c",
41: .id = 3,
42: .num_resources = ARRAY_SIZE(s3c_i2c_resource),
43: .resource = s3c_i2c_resource,
44: };
45:
46: void __init s3c_i2c3_set_platdata(struct s3c2410_platform_i2c *pd)
47: {
48: struct s3c2410_platform_i2c *npd;
49:
50: if (!pd) {
51: pd = &default_i2c_data;
52: pd->bus_num = 3;
53: }
54:
55: npd = s3c_set_platdata(pd, sizeof(struct s3c2410_platform_i2c),
56: &s3c_device_i2c3);
57:
58: if (!npd->cfg_gpio)
59: npd->cfg_gpio = s3c_i2c3_cfg_gpio;
60: }
然後會在arch/arm/mach-exynos/mach-tiny4412.c中註冊：
1: static struct platform_device *smdk4x12_devices[] __initdata = {
2: ... ...
3: &s3c_device_i2c3,
4: ... ...
5: }
6:
7: static void __init smdk4x12_machine_init(void)
8: {
9: ... ...
10: platform_add_devices(smdk4x12_devices, ARRAY_SIZE(smdk4x12_devices));
11: ... ...
12: }
I2C控制器對應的驅動是linux-3.0.86/drivers/i2c/busses/i2c-s3c2410.c。
三、移植
1、首先把MMA7660和I2C控制器的板級信息轉化為設備樹的形式，修改arch/arm/boot/dts/exynos4412-tiny4412.dts，添加MMA7660和I2C的硬體信息，可以參考內核文檔：Documentation/devicetree/bindings/i2c/i2c.txt和Documentation/devicetree/bindings/i2c/i2c-s3c2410.txt，中斷資源的填寫可以參考內核文檔Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt。
1: /* MMA7660FC */
2: &i2c_3 {
3: samsung,i2c-sda-delay = <100>;
4: samsung,i2c-slave-addr = <0x10>;
5: samsung,i2c-max-bus-freq = <200000>;
6: pinctrl-0 = <&i2c3_bus>;
7: pinctrl-names = "default";
8: status = "okay";
9:
10: mma7660@4c {
11: compatible = "freescale,mma7660";
12: reg = <0x4c>;
13: interrupt-parent = <&gpx3>;
14: interrupts = <1 2>;
15: poll_interval = <100>;
16: input_fuzz = <4>;
17: input_flat = <4>;
18: status = "okay";
19: };
20: };
上面的信息基本上是把原來的板級信息搬過來。
第13行和第14行是設置中斷資源，參考Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt：
External GPIO and Wakeup Interrupts:
The controller supports two types of external interrupts over gpio. The first
is the external gpio interrupt and second is the external wakeup interrupts.
The difference between the two is that the external wakeup interrupts can be
used as system wakeup events.
A. External GPIO Interrupts: For supporting external gpio interrupts, the
following properties should be specified in the pin-controller device node.
- interrupt-parent: phandle of the interrupt parent to which the external
GPIO interrupts are forwarded to.
- interrupts: interrupt specifier for the controller. The format and value of
the interrupt specifier depends on the interrupt parent for the controller.
In addition, following properties must be present in node of every bank
of pins supporting GPIO interrupts:
- interrupt-controller: identifies the controller node as interrupt-parent.
- #interrupt-cells: the value of this property should be 2.
- First Cell: represents the external gpio interrupt number local to the
external gpio interrupt space of the controller.
- Second Cell: flags to identify the type of the interrupt
- 1 = rising edge triggered
- 2 = falling edge triggered
- 3 = rising and falling edge triggered
- 4 = high level triggered
- 8 = low level triggered
對於interrupts = <1 2>，其中1表示GPX3_1，2表示的是下降沿觸發。
第2行的i2c_3是一個標號，i2c3的其他信息是在arch/arm/boot/dts/exynos4.dtsi中：
1: i2c_3: i2c@13890000 {
2: #address-cells = <1>;
3: #size-cells = <0>;
4: compatible = "samsung,s3c2440-i2c";
5: reg = <0x13890000 0x100>;
6: interrupts = <0 61 0>;
7: clocks = <&clock CLK_I2C3>;
8: clock-names = "i2c";
9: pinctrl-names = "default";
10: pinctrl-0 = <&i2c3_bus>;
11: status = "disabled";
12: };
第10行是設置GPIO的功能復用，i2c3_bus是在文件arch/arm/boot/dts/exynos4x12-pinctrl.dtsi中：
1: i2c3_bus: i2c3-bus {
2: samsung,pins = "gpa1-2", "gpa1-3";
3: samsung,pin-function = <3>;
4: samsung,pin-pud = <3>;
5: samsung,pin-drv = <0>;
6: };
那麼是在什麼時候解析這部分，然後設置功能復用的呢？這個以後再說。
2、填寫完板級信息，接下來就要移植驅動程式了，其中I2C控制器的驅動程式Linux內核已經寫好了，就是drivers/i2c/busses/i2c-s3c2410.c。MMA7660的驅動程式就需要我們自己移植了。
- 註冊
1: static const struct i2c_device_id mma7660_ids[] = {
2: { "mma7660", 0 },
3: { },
4: };
5: MODULE_DEVICE_TABLE(i2c, mma7660_ids);
6:
7: #ifdef CONFIG_OF
8: static const struct of_device_id mma7660_dt_match[] = {
9: { .compatible = "freescale,mma7660" },
10: { }
11: };
12: MODULE_DEVICE_TABLE(of, mma7660_dt_match);
13: #endif
14:
15: static struct i2c_driver mma7660_driver = {
16: .driver = {
17: .name = MMA7660_NAME,
18: .pm = &mma7660_pm_ops,
19: .of_match_table = of_match_ptr(mma7660_dt_match),
20: },
21: .probe = mma7660_probe,
22: .remove = mma7660_remove,
23: .id_table = mma7660_ids,
24: };
25:
26: module_i2c_driver(mma7660_driver);
- 解析設備樹
1: static struct mma7660_platform_data *mma7660_parse_dt(struct device *dev)
2: {
3: struct mma7660_platform_data *pdata;
4: struct device_node *np = dev->of_node;
5:
6: if (!np)
7: return NULL;
8:
9: pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
10: if (!pdata) {
11: dev_err(dev, "failed to allocate platform data\n");
12: return NULL;
13: }
14:
15: if (of_property_read_u32(np, "poll_interval", &pdata->poll_interval)) {
16: dev_err(dev, "failed to get poll_interval property\n");
17: return NULL;
18: }
19:
20: if (of_property_read_u32(np, "input_fuzz", &pdata->input_fuzz)) {
21: dev_err(dev, "failed to get input_fuzz property\n");
22: return NULL;
23: }
24:
25: if (of_property_read_u32(np, "input_flat", &pdata->input_flat)) {
26: dev_err(dev, "failed to get input_flat property\n");
27: return NULL;
28: }
29:
30: return pdata;
31: }
關於這部分我已經把代碼上傳到github上了，下載方法：
git clone https://github.com/pengdonglin137/linux-4.4_tiny4412.git -b port_to_tiny4412
測試
1: [root@tiny4412 root]# cd /sys/bus/i2c/devices/3-004c/
2: [root@tiny4412 3-004c]# ls
3: all_axis_g input of_node subsystem x_axis_g
4: driver modalias power tilt_status y_axis_g
5: hwmon name registers uevent z_axis_g
6: [root@tiny4412 3-004c]# cat all_axis_g
7: 2, 0, 22
8: [root@tiny4412 3-004c]# cat registers
9: REG: 0x00 = 0x03 ...... [ 0000 0011 ]
10: REG: 0x01 = 0x01 ...... [ 0000 0001 ]
11: REG: 0x02 = 0x16 ...... [ 0001 0110 ]
12: REG: 0x03 = 0x01 ...... [ 0000 0001 ]
13: REG: 0x04 = 0x02 ...... [ 0000 0010 ]
14: REG: 0x05 = 0xa0 ...... [ 1010 0000 ]
15: REG: 0x06 = 0xe7 ...... [ 1110 0111 ]
16: REG: 0x07 = 0x59 ...... [ 0101 1001 ]
17: REG: 0x08 = 0x49 ...... [ 0100 1001 ]
18: REG: 0x09 = 0x04 ...... [ 0000 0100 ]
19: REG: 0x0a = 0x0f ...... [ 0000 1111 ]
用hexdump看看上報的事件：
1: [root@tiny4412 ]# hexdump /dev/input/event0
2: 0000000 0013 0000 9b6a 0001 0003 0002 0015 0000
3: 0000010 0013 0000 9b6a 0001 0000 0000 0000 0000
4: 0000020 0013 0000 4015 0009 0003 0000 0002 0000
5: 0000030 0013 0000 4015 0009 0000 0000 0000 0000
6: 0000040 0018 0000 c6b5 000a 0003 0000 0004 0000
7: 0000050 0018 0000 c6b5 000a 0000 0000 0000 0000
8: 0000060 0019 0000 9ef7 0001 0003 0000 0006 0000
9: 0000070 0019 0000 9ef7 0001 0000 0000 0000 0000
10: 0000080 0019 0000 c6b3 000a 0003 0000 0005 0000
11: 0000090 0019 0000 c6b3 000a 0000 0000 0000 0000
12: 00000a0 0019 0000 d3f0 000d 0003 0000 0004 0000
13: 00000b0 0019 0000 d3f0 000d 0000 0000 0000 0000
14: 00000c0 001a 0000 25c1 0003 0003 0000 0003 0000
15: 00000d0 001a 0000 25c1 0003 0000 0000 0000 0000
16: 00000e0 001a 0000 32d0 0006 0003 0000 0002 0000
17: 00000f0 001a 0000 32d0 0006 0000 0000 0000 0000
18: 0000100 001a 0000 b980 0007 0003 0000 0001 0000
19: 0000110 001a 0000 b980 0007 0000 0000 0000 0000
未完待續…
