linux-kernel - Re: [PATCH v4 2/5] ACPI / processor_idle: Add support for Low Power Idle(LPI) states

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Date:	Tue, 10 May 2016 02:04:41 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Al Stone <al.stone@...aro.org>,
	Prashanth Prakash <pprakash@...eaurora.org>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>
Subject: Re: [PATCH v4 2/5] ACPI / processor_idle: Add support for Low Power Idle(LPI) states

On Tuesday, April 19, 2016 01:30:10 PM Sudeep Holla wrote:
> ACPI 6.0 introduced an optional object _LPI that provides an alternate
> method to describe Low Power Idle states. It defines the local power
> states for each node in a hierarchical processor topology. The OSPM can
> use _LPI object to select a local power state for each level of processor
> hierarchy in the system. They used to produce a composite power state
> request that is presented to the platform by the OSPM.
> 
> Since multiple processors affect the idle state for any non-leaf hierarchy
> node, coordination of idle state requests between the processors is
> required. ACPI supports two different coordination schemes: Platform
> coordinated and  OS initiated.
> 
> This patch adds initial support for Platform coordination scheme of LPI.
> 
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/acpi/bus.c              |  11 +-
>  drivers/acpi/processor_driver.c |   2 +-
>  drivers/acpi/processor_idle.c   | 441 +++++++++++++++++++++++++++++++++++-----
>  include/acpi/processor.h        |  25 ++-
>  include/linux/acpi.h            |   4 +
>  5 files changed, 422 insertions(+), 61 deletions(-)
> 
> Hi Rafael,
> 
> Yet to be discussed(retained as in from previous version):

I somehow didn't realize that you had been waiting for my feedback.  Sorry
about that.

> - Kconfig entry removal: Need feedback on how to deal with that
>   without having to introduce dummy _CST related ARM64 callbacks
> - Didn't defer processing of LPI buffers to flattening as it
>   results in the same buffer decoded multiple times
> - ACPI_CSTATE_INTEGER : IMO it's reasonable to keep it aroundsince the
>   it's part of LPI specification(not just ARM FFH)

OK, I'll have a look tomorrow.

Thanks,
Rafael