Device Power State
Device Power State I will be describing about only Native Power management here, where we will set the PM configuration hardware registers through PCI configuration space. Well there are other kinds of PM like runtime PM, Native PM using firmware like ACPI..etc What is Device Power State ? In general, power management is a feature allowing one to save energy by putting devices into states in which they draw less power (low-power states) at the price of reduced functionality or performance. PCI devices may be put into low-power states in two ways, by using the device capabilities introduced by the PCI Bus Power Management Interface Specification, or with the help of platform firmware, such as an ACPI BIOS. In the first approach, that is referred to as the native PCI power management (native PCI PM) in what follows, the device power state is changed as a result of writing a specific value into one of its standard configuration registers. The second approach requires the platform firm