linux-kernel - [RFC PATCH 0/4] Support for passing runtime state idle time to TF-A

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Message-ID: <1619123448-10138-1-git-send-email-skomatineni@nvidia.com>
Date:   Thu, 22 Apr 2021 13:30:44 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     <sudeep.holla@....com>, <souvik.chakravarty@....com>,
        <thierry.reding@...il.com>, <skomatineni@...dia.com>,
        <mark.rutland@....com>, <lorenzo.pieralisi@....com>,
        <daniel.lezcano@...aro.org>, <robh+dt@...nel.org>
CC:     <jonathanh@...dia.com>, <ksitaraman@...dia.com>,
        <sanjayc@...dia.com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-pm@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: [RFC PATCH 0/4] Support for passing runtime state idle time to TF-A

Tegra194 and Tegra186 platforms use separate MCE firmware for CPUs which is
in charge of deciding on state transition based on target state, state idle
time, and some other Tegra CPU core cluster states information.

Current PSCI specification don't have function defined for passing runtime
state idle time predicted by governor (based on next events and state target
residency) to ARM trusted firmware.

With the support of adding new PSCI function to allow passing runtime state
idle time from kernel to ARM trusted firmware, Tegra194 platforms can use
generic psci cpuidle driver rather than having Tegra specific cpuidle driver.

During Tegra specific cpuidle driver V1 review, Sudeep Holla from ARM also
suggested to use generic cpuidle driver by generalizing the need of runtime
state idle time.

So had internal discussion between ARM and NVIDIA on adding new PSCI function
to allow passing runtime state idle time from kernel to TF-A through PSCI and
once this implementation is accepted by upstream, ARM will look into further
to update PSCI specification for this new PSCI function.

So sending these patches as RFC as new PSCI function added in this series is
not part of PSCI specification and once this implementation is accepted by ARM
and upstream community, ARM can help to take this forward to add to PSCI
specification.

To keep the backward compatibility we can't update CPU_SUSPEND function to pass
state idle time argument. So added seperate function for passing state idle time
and serializing this with cpu suspend state enter.

Once this approach is agreed, we can either use this way of separate PSCI
function for passing state idle time or with PSCI specification update we can
use same CPU_SUSPEND function with extra argument for state idle time which can
be decided later for final patches based on discussion with ARM.

Sowjanya Komatineni (4):
  firmware/psci: add support for PSCI function SET_STATE_IDLE_TIME
  cpuidle: menu: add idle_time to cpuidle_state
  cpuidle: psci: pass state idle time before state enter callback
  arm64: dts: tegra194: Add CPU idle states

 arch/arm64/boot/dts/nvidia/tegra194.dtsi | 19 +++++++++++++++++++
 drivers/cpuidle/cpuidle-psci.c           | 11 +++++++++++
 drivers/cpuidle/governors/menu.c         |  7 ++++++-
 drivers/firmware/psci/psci.c             |  9 +++++++++
 include/linux/cpuidle.h                  |  1 +
 include/linux/psci.h                     |  1 +
 include/uapi/linux/psci.h                |  2 ++
 7 files changed, 49 insertions(+), 1 deletion(-)

-- 
2.7.4