-
A.whenever a device is registered on a bus, the kernel has to run the match function to find a matching driver. If there is a match the probe function of that driver is invoked.

MODULE_DEVICE_TABLE is used by the driver to tell kernel what kind of device it can support.At compilation time, the build process extracts
this information out of the driver and builds a table.

How device tree and driver matches

arch/arm/boot/dts/am335x-boneblack-common.dtsi
there is an i2c node

&i2c0 {
tda19988: tda19988 {
compatible = "nxp,tda998x";
reg = <0x70>;
.....
}

go to /home/mrigendra.chaubey/bbb/linux-4.4_prct/drivers/gpu/drm/i2c/tda998x_drv.c

this file declares ,

#ifdef CONFIG_OF
static const struct of_device_id tda998x_dt_ids[] = {
{ .compatible = "nxp,tda998x", },<------
{ }
};
MODULE_DEVICE_TABLE(of, tda998x_dt_ids);
#endif

static struct i2c_device_id tda998x_ids[] = {
{ "tda998x", 0 },<----------
{ }
};

So we can see that device properties are there in device .dtsi file and corresponding driver which supports this device is in driver directory of the kernel.When kernel gets this node it searches in a table for the driver and matches with this driver, and then probe is called.

b.
for platform drvier example check this one
/home/mrigendra.chaubey/bbb/linux-4.4/drivers/leds/leds-gpio.c
and
/home/mrigendra.chaubey/bbb/linux-4.4/arch/arm/boot/dts/am335x-bone-common.dtsi

check gpio-leds in compatible field
leds {
pinctrl-names = "default", "sleep";
pinctrl-0 = <&user_leds_default>;
pinctrl-1 = <&user_leds_sleep>;

compatible = "gpio-leds";

led@2 {
label = "beaglebone:green:usr0";
gpios = <&gpio1 21 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "heartbeat";
default-state = "off";
};

led@3 {
label = "beaglebone:green:usr1";
gpios = <&gpio1 22 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "mmc0";
default-state = "off";
};

led@4 {
label = "beaglebone:green:usr2";
gpios = <&gpio1 23 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "cpu0";
default-state = "off";
};

led@5 {
label = "beaglebone:green:usr3";
gpios = <&gpio1 24 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "mmc1";
default-state = "off";
};
};

Comments

Post a Comment

Popular posts from this blog

dev_get_platdata understanding

-
So I see this type of code in platform driver inside kernel, struct gpio_led_platform_data *pdata = dev_get_platdata(&pdev->dev); or this, struct aat2870_platform_data *pdata = dev_get_platdata(&client->dev); So how dev_ get_platdata is helping us. In device.h the definition here is, static inline void *dev_get_platdata(const struct device *dev) { return dev->platform_data; } So if I see from kernel it is always done for to get platform specific data. Like Here is a definition of platform_device, in platform_device.h struct platform_device { const char *name; int id; bool id_auto; struct device dev;  <-------------------- u32 num_resources; struct resource *resource; const struct platform_device_id *id_entry; char *driver_override; /* Driver name to force a match */ /* MFD cell pointer */ struct mfd_cell *mfd_cell; /* arch specific additions */ struct pdev_archdata archdata; }; further struct devic...
Read more

How to take systrace in android

-
Image
Install python 2.7 . As systrace does not support python 3.6. Python has its own package manager 'pip'. Use it to install new packages.         download python2.7 install pywin32 and six module on windows. Open power shell in C:/Python27/Scripts path,          pip install pywin32          pip install six   Above packages are not required to be installed on Ubuntu. But if you want other packages of python, we have to install python-pip, however not required for systrace.           sudo apt install python-pip        Then do pip list to see what packages are installed in Ubuntu. Install android studio        Start android studio from the downloaded android studio. That will        have a script to start an...
Read more

Getting started with pinctrl subsystem linux

-
A pin controller is a piece of hardware, usually a set of registers, that can control PINs. It may be able to multiplex, bias, set load capacitance, set drive strength, etc. for individual pins or groups of pins.   PINMUX   PINCONF - electronic properties e.g. high impedance, tristate, input pin to VDD or GND using a certain resistor value - pull up and pull down so that the pin has a stable value when nothing is driving the rail it is connected to, or when it’s unconnected. Pin configuration can be programmed by adding configuration entries into the mapping table     say that we have a group of pins dealing with an SPI interface on { 0, 8, 16, 24 }, and a group of pins dealing with an I2C interface on pins on { 24, 25 }.   make a group static const unsigned int spi0_pins[] = { 0, 8, 16, 24 }; static const unsigned int i2c0_pins[] = { 24, 25 }; //combine them  static const struct foo_group foo_groups[] = { { .name = "spi0_grp", ...
Read more