Re: [Linaro-acpi] [PATCH v7 5/8] CPPC: Add a CPUFreq driver for use with CPPC

Hi Rafael,

On 21/07/15 15:27, Rafael J. Wysocki wrote:

Hi Sudeep,

On Tue, Jul 21, 2015 at 10:52 AM, Sudeep Holla sudeep.holla@arm.com wrote:

...

On 20/07/15 23:07, Rafael J. Wysocki wrote:

...

On Monday, July 20, 2015 03:22:09 PM Sudeep Holla wrote:

...

On 09/07/15 19:04, Ashwin Chaugule wrote:

...

This driver utilizes the methods introduced in the previous patch - "ACPI: Introduce CPU performance controls using CPPC" and enables usage with existing CPUFreq governors.

Signed-off-by: Ashwin Chaugule ashwin.chaugule@linaro.org Reviewed-by: Al Stone al.stone@linaro.org

---

drivers/cpufreq/Kconfig.arm    |  16 ++++
drivers/cpufreq/Makefile       |   2 +
drivers/cpufreq/cppc_cpufreq.c | 197

+++++++++++++++++++++++++++++++++++++++++ 3 files changed, 215 insertions(+) create mode 100644 drivers/cpufreq/cppc_cpufreq.c

diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm index 4f3dbc8..578384d 100644 --- a/drivers/cpufreq/Kconfig.arm +++ b/drivers/cpufreq/Kconfig.arm @@ -272,3 +272,19 @@ config ARM_PXA2xx_CPUFREQ This add the CPUFreq driver support for Intel PXA2xx SOCs.

       If in doubt, say N.

+config ACPI_CPPC_CPUFREQ

•   tristate "CPUFreq driver based on the ACPI CPPC spec"
  

•   depends on ACPI_CPPC_LIB
  

•   default n
  

•   help
  

•     This adds a CPUFreq driver which uses CPPC methods
  

•     as described in the ACPIv5.1 spec. CPPC stands for
  

•     Collaborative Processor Performance Controls. It
  

•     is based on an abstract continuous scale of CPU
  

•     performance values which allows the remote power
  

•     processor to flexibly optimize for power and
  

•     performance. CPPC relies on power management firmware
  

•     for its operation.
  

Why is this ARM specific ? It might be used only on ARM but doesn't mean it should be visible only on ARM ACPI systems.

Why bother people with considering Kconfig options that are useless to them?

I agree to some extent, but main worry is that we are then making these features architecture specific while ACPI is supposed to be architecture agnostic. I was just trying to avoid doing so.

Problem is, there are no plans to support CPPC on x86 in Linux I'm aware of and so we should not use it even if it is exposed by the firmware (Windows may be using it, though).

Ah that makes sense.

I'm also not aware of plans to support _PSS on ARM.

Agreed, but you never know what ARM vendors can do :)

So, even though on the spec level they are arch-independent, the way we use those interfaces in the kernel isn't.

Understood.

Regards, Sudeep