Driver Model (USB,I2C) enumerate device and bind it with driver .USB and PCI are hotplugged device and they have capability to notify OS when lets say USB (pendrive )attach.But in SOC’s based , a lot of inbuilt peripherals like host controller(eg i2c HC) these inbuilt devices are not capable to inform the OS that they are present. So the kernel/drivers developers built similar model like hot pluggable devices so they invented platform drivers model.
Linux kernel exports a general functionality for devices directly attached to processor without any bus/bus controller. For such devices a general data/syfs structure called platform driver is defined so that they can be attached to Device driver Model.