This document discusses platform device drivers in Linux. It describes the components of platform device drivers, including platform drivers and platform devices. It explains how to register a platform driver, register a platform device, bind a driver to a device, specify platform resources and data. It also discusses using device tree bindings with platform drivers and summarizes the key topics covered.

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Platform Device Drivers

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What to Expect?
W's of Platform Device Drivers
Registering a Platform Driver
Registering a Platform Device
Binding a platform driver to a device
Platform resources and platform data
Testing a simple platform driver

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W's of Platform Device Drivers
Provides a mechanism to notify the kernel of
available hardware on the board
Mechanism to add the devices to the device
model of the kernel
Used for non-discoverable devices
Driver for the devices on the virtual 'platform' bus

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Components of Platform Device
Drivers
Two components
Platform Driver
Set of operations done on the device
Platform Device
Information about the device
Deemed to be connected to a virtual 'platform' bus

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Platform Bus Drivers Registration
platform_device.h
platform_driver structure defined as below:
struct platform_driver
int (*probe)(struct platform_device *);
int (*remove)(struct platform_device *);
void (*shutdown)(struct platform_device *);
int (*suspend)(struct platform_device *, pm_message_t state);
int (*resume)(struct platform_device *);
At minimum, probe() & remove needs to be supplied
int platform_driver_register(struct platform_driver *)

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Platform Device Registration
Defined by board specific file
platform_device.h
platform_device structure defined as below:
const char *name
int id
struct resource *resource
const struct platform_device_id *id_entry
int platform_device_register(struct platform_device
*pdev)

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Binding the Driver with Device
Mechanism for bus code to attach a driver to
device
id_table
struct platform_device_id
char name[PLATFORM_NAME_SIZE]
kernel_ulong_t driver_data
Name of driver, specified in the name field

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Specifying the Resource Info
For providing the information such as memory locations, IRQ numbers etc
struct resource my_resource [] = {
{
.start = RESOURCE_START_ADDRESS,
.end = RESOURCE_END_ADDRESS,
.flags = IORESOURCE_MEM
}
}
struct platform_device my_device = {
.name = DRIVER_NAME,
.num_resources = ARRAY_SIZE(my_resource),
.resources = my_resource,
}

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Platform Data
Mechanism to pass the generic device specific
information from Platform Device to the Platform Driver
Example – Passing GPIO information
int gpio_led = 53;
struct platform_device led_device {
name = DRIVER_NAME,
.dev = {
.platform_data = &gpio_led,
}
}

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Platform Driver With DTB
const struct of_device_id gpio_led_dt[] = {
{ .compatible = "my-led", },
{ }
};
of_property_read_u32(np, "led-number",
&gpio_number);
.of_match_table = of_match_ptr(gpio_led_dt);

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What all we Learnt?
W's of Platform Device Drivers
Registering a Platform Driver
Registering a Platform Device
Binding a platform driver to a device
Platform resources and platform data
Testing a simple platform driver

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Any Queries?