admin-guide/pm/cpufreq_drivers.rst

80 ``pcc-cpufreq``
86   *  pcc-cpufreq.txt - PCC interface documentation
100  1.1	PCC interface
113  Processor Clocking Control (PCC) is an interface between the platform
117  The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC
120  OS utilizes the PCC interface to inform platform firmware what frequency the
126  1.1 PCC interface:
128  The complete PCC specification is available here:
131  PCC relies on a shared memory region that provides a channel for communication
132  between the OS and platform firmware. PCC also implements a "doorbell" that
136  The ACPI PCCH() method is used to discover the location of the PCC shared
141  The following commands are supported by the PCC interface:
149  When PCC mode is enabled, the platform will not expose processor performance
156  The PCC driver fills in the command interface, and the input buffer and
160  Each PCC command is "global" in scope and can affect all the logical CPUs in
161  the system. Therefore, PCC is capable of performing "group" updates. With PCC
182  The PCC driver will load on any system where the platform firmware:
183  * supports the PCC interface, and the associated PCCH() and PCCP() methods
187  Currently, certain HP ProLiant platforms implement the PCC interface. On those
188  platforms PCC is the "default" choice.
191  such an instance, as is also the case on platforms where the PCC interface
192  is not implemented, the PCC driver will fail to load silently.
199  The PCC driver loads with a message such as:
200  pcc-cpufreq: (v1.00.00) driver loaded with frequency limits: 1600 MHz, 2933
214      |-- this is the version of the PCC specification the driver adheres to
218  /sys filesystem and how their values are affected by the PCC driver:
229  The cpuinfo_transition_latency field is 0. The PCC specification does
266  Currently, the PCC driver does not evaluate _PSD. The platforms that support
267  PCC do not implement SW_ALL. So OSPM doesn't need to perform any coordination
273  expected to work with the PCC driver. Since the "cpufreq_stats" module
274  provides information wrt each P-state, it is not applicable to the PCC driver.