linux-kernel - Re: [PATCH v6 00/18] Consolidate and improve NVIDIA Tegra CPUIDLE driver(s)

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Message-ID: <20191016192133.GB26038@pdeschrijver-desktop.Nvidia.com>
Date:   Wed, 16 Oct 2019 22:21:33 +0300
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>
CC:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Daniel Lezcano" <daniel.lezcano@...aro.org>,
        <linux-pm@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 00/18] Consolidate and improve NVIDIA Tegra CPUIDLE
 driver(s)

On Tue, Oct 15, 2019 at 07:59:57PM +0300, Dmitry Osipenko wrote:
> Hello,
> 
> This series does the following:
> 
>   1. Unifies Tegra20/30/114 drivers into a single driver and moves it out
>      into common drivers/cpuidle/ directory.
> 
>   2. Enables CPU cluster power-down idling state on Tegra30.
> 
> In the end there is a quite nice clean up of the Tegra CPUIDLE drivers
> and of the Tegra's arch code in general. Please review, thanks!
> 
> Changelog:
> 
> v6: - Addressed request from Thierry Reding to change the way patches are
>       organized by making changes in a more incremental manner.
> 
>     - tegra_sleep_cpu() now checks for the secondary CPUs to be offline
>       in the "Make outer_disable() open-coded" patch.
> 
> v5: - Rebased on a recent linux-next, fixed one minor conflict in Kconfig.
> 
>     - Improved commit's message of the "Support CPU cluster power-down state
>       on Tegra30" patch.
> 
>     - The "Support CPU cluster power-down state on Tegra30" patch is also
>       got split and now there is additional "Make outer_disable() open-coded"
>       patch.
> 
>     - Made minor cosmetic changes to the "Introduce unified driver for
>       NVIDIA Tegra SoCs" patch by improving error message and renaming
>       one variable.
> 
> v4: - Fixed compilation with !CONFIG_CACHE_L2X0 (and tested that it still
>       works).
> 
>     - Replaced ktime_compare() with ktime_before() in the new driver,
>       for consistency.
> 
> v3: - Addressed review comments that were made by Jon Hunter to v2 by
>       splitting patches into smaller (and simpler) chunks, better
>       documenting changes in the commit messages and using proper error
>       codes in the code.
> 
>       Warnings are replaced with a useful error messages in the code of
>       "Introduce unified driver for NVIDIA Tegra SoCs" patch.
> 
>       Secondary CPUs parking timeout increased to 100ms because I found
>       that it actually may happen to take more than 1ms if CPU is running
>       on a *very* low frequency.
> 
>       Added diagnostic messages that are reporting Flow Controller state
>       when CPU parking fails.
> 
>       Further polished cpuidle driver's code.
> 
>       The coupled state entering is now aborted if there is a pending SGI
>       (Software Generated Interrupt) because it will be lost after GIC's
>       power-cycling. Like it was done by the old Tegra20 CPUIDLE driver.
> 
> v2: - Added patches to enable the new cpuidle driver in the defconfigs:
> 
>         ARM: multi_v7_defconfig: Enable Tegra cpuidle driver
>         ARM: tegra: Enable Tegra cpuidle driver in tegra_defconfig
> 
>     - Dropped patches that removed CPUIDLE_FLAG_TIMER_STOP from the idling
>       states because that flag actually doesn't have any negative effects,
>       but still is correct for the case of a local CPU timer on older Tegra
>       SoCs:
> 
>         cpuidle: tegra: Remove CPUIDLE_FLAG_TIMER_STOP from Tegra114/124 idle-state
>         cpuidle: tegra: Remove CPUIDLE_FLAG_TIMER_STOP from all states
> 
>     - The "Add unified driver for NVIDIA Tegra SoCs" patch got more polish.
>       Tegra30 and Terga114 states are now squashed into a single common C7
>       state (following Parker TRM terminology, see 17.2.2.2 Power Management
>       States), more comments added, etc minor changes.

It would be useful to switch the power state terminology to the one used
for later chips:

LP0 becomes SC7
LP1 becomes C1
LP2 becomes CC7

Meaning of these states is as follows

C is a core state:

C1 clock gating
C2 not defined
C3 not defined
C4 not defined
C5 not defined
C6 not defined for ARM cores
C7 power-gating

CC is a CPU cluster C state:

CC1 cluster clock gated
CC2 not defined
CC3 fmax@...n: not used prior to Tegra186
CC4: cluster retention: no longer supported
CC5: not defined
CC6: cluster power gating
CC7: cluster rail gating

SC is a System C state:

SC1: not defined
SC2: not defined
SC3: not defined
SC4: not defined
SC5: not defined
SC6: not defined
SC7: VDD_SOC off

Cheers,

Peter.