cpufreq: intel_pstate: Disable energy efficiency optimization

Some Kabylake desktop processors may not reach max turbo when running in
HWP mode, even if running under sustained 100% utilization.

This occurs when the HWP.EPP (Energy Performance Preference) is set to
"balance_power" (0x80) -- the default on most systems.

It occurs because the platform BIOS may erroneously enable an
energy-efficiency setting -- MSR_IA32_POWER_CTL BIT-EE, which is not
recommended to be enabled on this SKU.

On the failing systems, this BIOS issue was not discovered when the
desktop motherboard was tested with Windows, because the BIOS also
neglects to provide the ACPI/CPPC table, that Windows requires to enable
HWP, and so Windows runs in legacy P-state mode, where this setting has
no effect.

Linux' intel_pstate driver does not require ACPI/CPPC to enable HWP, and
so it runs in HWP mode, exposing this incorrect BIOS configuration.

There are several ways to address this problem.

First, Linux can also run in legacy P-state mode on this system.
As intel_pstate is how Linux enables HWP, booting with
"intel_pstate=disable"
will run in acpi-cpufreq/ondemand legacy p-state mode.

Or second, the "performance" governor can be used with intel_pstate,
which will modify HWP.EPP to 0.

Or third, starting in 4.10, the
/sys/devices/system/cpu/cpufreq/policy*/energy_performance_preference
attribute in can be updated from "balance_power" to "performance".

Or fourth, apply this patch, which fixes the erroneous setting of
MSR_IA32_POWER_CTL BIT_EE on this model, allowing the default
configuration to function as designed.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Cc: 4.6+ <stable@vger.kernel.org> # 4.6+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

path: root/sound/atmel/Kconfig

menu "Atmel devices (AVR32 and AT91)"
	depends on AVR32 || ARCH_AT91

config SND_ATMEL_ABDAC
	tristate "Atmel Audio Bitstream DAC (ABDAC) driver"
	select SND_PCM
	depends on DW_DMAC && AVR32
	help
	  ALSA sound driver for the Atmel Audio Bitstream DAC (ABDAC).

config SND_ATMEL_AC97C
	tristate "Atmel AC97 Controller (AC97C) driver"
	select SND_PCM
	select SND_AC97_CODEC
	depends on (DW_DMAC && AVR32) || ARCH_AT91
	help
	  ALSA sound driver for the Atmel AC97 controller.

endmenu