For compile time configuration, it’s common Linux practice to keep board- and application-specific configuration out of the main driver file, instead putting it into the board support file.

For devices on custom boards, as typical of embedded and SoC-(system-on-chip) based hardware, Linux uses platform_data to point to board-specific structures describing devices and how they are connected to the SoC. This can include available ports, chip variants, preferred modes, default initialization, additional pin roles, and so on. This shrinks the board-support packages (BSPs) and minimizes board and application specific #ifdefs in drivers.

21 Oct 2010 16:10

platform_data: Platform data specific to the ADP1650 device.
Includes feature selections and default initialization.

Please see include/linux/i2c/adp1650.h for details.

#include 
?
static struct adp1650_leds_platform_data adp1650_pdata = {
	.timer_iocfg = 	ADP1650_IOCFG_IO2_HIGH_IMP |
			ADP1650_IOCFG_IO1_TORCH |
			ADP1650_FL_TIMER_ms(500),
?
	.current_set = 	ADP1650_I_FL_mA(900) |
			ADP1650_I_TOR_mA(100),
?
	.output_mode = 	ADP1650_IL_PEAK_2A25 |
			ADP1650_STR_LV_EDGE |
			ADP1650_FREQ_FB_EN |
			ADP1650_OUTPUT_EN |
			ADP1650_STR_MODE_HW |
			ADP1650_STR_MODE_STBY,
?
	.control = 	ADP1650_I_TX2_mA(400) |
			ADP1650_I_TX1_mA(400),
?
	.ad_mode =	ADP1650_DYN_OVP_EN |
			ADP1650_STR_POL_ACTIVE_HIGH |
			ADP1650_I_ILED_2mA75 |
			ADP1650_IL_DC_1A50 |
			ADP1650_IL_DC_EN,
?
	.batt_low =	ADP1650_CL_SOFT_EN |
			ADP1650_I_VB_LO_mA(400) |
			ADP1650_V_VB_LO_3V50,
?
	.gpio_enable = -1,
};

Declaring I2C devices

Unlike PCI or USB devices, I2C devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each I2C bus segment, and what address these devices are using. For this reason, the kernel code must instantiate I2C devices explicitly. There are different ways to achieve this, depending on the context and requirements. However the most common method is to declare the I2C devices by bus number.

This method is appropriate when the I2C bus is a system bus, as in many embedded systems, wherein each I2C bus has a number which is known in advance. It is thus possible to pre-declare the I2C devices that inhabit this bus. This is done with an array of struct i2c_board_info, which is registered by calling i2c_register_board_info().

So, to enable such a driver one need only edit the board support file by adding an appropriate entry to i2c_board_info.

For more information see: Documentation/i2c/instantiating-devices

21 Oct 2010 16:10

static struct i2c_board_info __initdata board_i2c_board_info[] = {
#if defined(CONFIG_LEDS_ADP1650) || defined(CONFIG_LEDS_ADP1650_MODULE)
	{
		I2C_BOARD_INFO("adp1650", 0x30),
		.platform_data = (void *)&adp1650_pdata,
	},
#endif
};

static int __init board_init(void)
{
	[--snip--]
?
	i2c_register_board_info(0, board_i2c_board_info,
				ARRAY_SIZE(board_i2c_board_info));
	[--snip--]
?
	return 0;
}
arch_initcall(board_init);

Adding Linux driver support

Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)

The ADP1650 LED driver depends on I2C.

Device Drivers  --->
	[*] LED Support  ---> 
		--- LED Support
		[*]   LED Class Support
			* LED drivers *

		<--snip-->
		<*>   LED Support for ADP1650 I2C chips
		<--snip-->

Driver testing

LED handling under Linux

The LED class allows control of LEDs from userspace. LEDs appear in /sys/class/leds/. The brightness file will set the brightness of the LED (taking a value 0-255).

For more information read linux/Documentaion/leds-class.txt

brightness: get/set LED brightness (an integer between 0 and 255)
max_brightness: the maximum brightness value.

Driver specific brightness interpretation

Value	Define	Description	Intensity
0	FL_MODE_OFF	Turns LED/FLASH off	0
1	FL_MODE_TORCH_25mA	Software initiated TORCH/Assist light	25mA
2	FL_MODE_TORCH_50mA	(STROBE) triggers FLASH	50mA
3	FL_MODE_TORCH_75mA		75mA
4	FL_MODE_TORCH_100mA		100mA
5	FL_MODE_TORCH_125mA		125mA
6	FL_MODE_TORCH_150mA		150mA
7	FL_MODE_TORCH_175mA		175mA
8	FL_MODE_TORCH_200mA		200mA
9	FL_MODE_TORCH_TRIG_EXT_25mA	Hardware (GPIO1) triggered TORCH/Assist light	25mA
10	FL_MODE_TORCH_TRIG_EXT_50mA	(STROBE) triggers FLASH	50mA
11	FL_MODE_TORCH_TRIG_EXT_75mA		75mA
12	FL_MODE_TORCH_TRIG_EXT_100mA		100mA
13	FL_MODE_TORCH_TRIG_EXT_125mA		125mA
14	FL_MODE_TORCH_TRIG_EXT_150mA		150mA
15	FL_MODE_TORCH_TRIG_EXT_175mA		175mA
16	FL_MODE_TORCH_TRIG_EXT_200mA		200mA
254	FL_MODE_FLASH	Software initiated LED FLASH	I_FL
255	FL_MODE_FLASH_TRIG_EXT	Hardware (STROBE) triggered LED FLASH	I_FL