Re: [PATCH v6 2/7] ACPI: Make ACPI processor driver more extensible

Hi Rafael,

On 8 July 2015 at 09:34, Rafael J. Wysocki [off-list ref] wrote:

Hi Ashwin,

On Wed, Jul 8, 2015 at 3:27 AM, Ashwin Chaugule
[off-list ref] wrote:

quoted

On 7 July 2015 at 21:07, Rafael J. Wysocki [off-list ref] wrote:

quoted

On Monday, June 15, 2015 04:09:06 PM Ashwin Chaugule wrote:

quoted

The ACPI processor driver is currently tied too closely
to the ACPI C-states (CST), P-states (PSS) and other related
constructs for controlling CPU idle and CPU performance.

The newer ACPI specification (v5.1 onwards) introduces
alternative methods to CST and PSS. These new mechanisms
are described within each ACPI Processor object and so they
need to be scanned whenever a new Processor object is detected.
This patch introduces two new Kconfig symbols to allow for
finer configurability among the various options for controlling
CPU idle and performance states. There is no change in functionality
and these options are defaulted to enabled to maintain previous
behaviour.

The following patchwork introduces CPPC: A newer method of
controlling CPU performance. The OS is not expected to support CPPC
and PSS at runtime. So the kconfig option lets us make these two
mutually exclusive at compile time.

Signed-off-by: Ashwin Chaugule <redacted>
Reviewed-by: Al Stone <redacted>
---
 drivers/acpi/Kconfig            |  31 +++++++++--
 drivers/acpi/Makefile           |   7 ++-
 drivers/acpi/processor_driver.c |  86 ++++++++++++++++++----------
 drivers/cpufreq/Kconfig         |   2 +-
 drivers/cpufreq/Kconfig.x86     |   2 +
 include/acpi/processor.h        | 120 ++++++++++++++++++++++++++++------------
 6 files changed, 176 insertions(+), 72 deletions(-)

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index ab2cbb5..5942754 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig

@@ -166,18 +166,39 @@ config ACPI_DOCK
        This driver supports ACPI-controlled docking stations and removable
        drive bays such as the IBM Ultrabay and the Dell Module Bay.

-config ACPI_PROCESSOR
-     tristate "Processor"
-     select THERMAL
-     select CPU_IDLE
+config ACPI_CST
+     bool "ACPI C states (CST) driver"
+     depends on ACPI_PROCESSOR
      depends on X86 || IA64
+     select CPU_IDLE
      default y
      help
        This driver installs ACPI as the idle handler for Linux and uses
        ACPI C2 and C3 processor states to save power on systems that
-       support it.  It is required by several flavors of cpufreq
+       support it.
+
+config ACPI_PSS
+     bool "ACPI P States (PSS) driver"
+     depends on ACPI_PROCESSOR
+     depends on X86 || IA64
+     select THERMAL
+     default y
+     help
+       This driver implements ACPI methods for controlling CPU performance
+       using PSS methods as described in the ACPI spec. It also enables support
+       for ACPI based performance throttling (TSS) and ACPI based thermal
+       monitoring. It is required by several flavors of cpufreq
        performance-state drivers.

For starters, I don't like these new Kconfig options.

Isn't there a way to implement what you need without adding them?

We need to use the ACPI Processor driver for CPPC without including
all its current dependencies. (i.e. PSS, TSS, CSS etc.). The upcoming
LPI work from Sudeep will also face the same issue. I considered the
alternative of adding a probe routine which matches
ACPI_PROCESSOR_OBJECT/DEVICE_HID to each driver, but this seemed like
a better option. Do you have any other ideas?

First of all, I don't see what _CST has to do with CPPC.

Second, it looks like the problem is that x86 probably won't use CPPC,
while arm64 probably won't use _PSS.

That can be addressed by adding Kconfig options, but those options
should not be user-selectable (because quite honestly users don't have
to know what those things are and they don't care *and* things break
if they make a wrong choice).  Instead, I'd make architecture Kconfigs
select those options automatically.

I've made changes locally. Basically s/ACPI_PSS/HAVE_ACPI_PSS/ and in
arch/x86/Kconfig; select HAVE_ACPI_PSS if ACPI. Similarly for CST.
Just wanted to check if there were any other comments before sending
out v7.

Thanks,
Ashwin.