linux-kernel - Re: [PATCH 0/6] ARM: psci: cpuidle: PSCI CPUidle rework

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Message-ID: <20190723141905.GB22025@e121166-lin.cambridge.arm.com>
Date:   Tue, 23 Jul 2019 15:19:05 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Linux PM <linux-pm@...r.kernel.org>, Will Deacon <will@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        LKML <linux-kernel@...r.kernel.org>,
        LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 0/6] ARM: psci: cpuidle: PSCI CPUidle rework

On Tue, Jul 23, 2019 at 01:49:15PM +0200, Ulf Hansson wrote:
> On Mon, 22 Jul 2019 at 17:37, Lorenzo Pieralisi
> <lorenzo.pieralisi@....com> wrote:
> >
> > Current PSCI CPUidle driver is built on top of the generic ARM
> > CPUidle infrastructure that relies on the architectural back-end
> > idle operations to initialize and enter idle states.
> >
> > On ARM64 systems, PSCI is the only interface the kernel ever uses
> > to enter idle states, so, having to rely on a generic ARM CPUidle
> > driver when there is and there will always be only one method
> > for entering idle states proved to be overkill, more so given
> > that on ARM 32-bit systems (that can also enable the generic
> > ARM CPUidle driver) only one additional idle back-end was
> > ever added:
> >
> > drivers/soc/qcom/spm.c
> >
> > and it can be easily converted to a full-fledged CPUidle driver
> > without requiring the generic ARM CPUidle framework.
> >
> > Furthermore, the generic ARM CPUidle infrastructure forces the
> > PSCI firmware layer to keep CPUidle specific information in it,
> > which does not really fit its purpose that should be kernel
> > control/data structure agnostic.
> >
> > Lastly, the interface between the generic ARM CPUidle driver and
> > the arch back-end requires an idle state index to be passed to
> > suspend operations, with idle states back-end internals (such
> > as idle state parameters) hidden in architectural back-ends and
> > not available to the generic ARM CPUidle driver.
> >
> > To improve the above mentioned shortcomings, implement a stand
> > alone PSCI CPUidle driver; this improves the current kernel
> > code from several perspective:
> >
> > - Move CPUidle internal knowledge into CPUidle driver out of
> >   the PSCI firmware interface
> > - Give the PSCI CPUidle driver control over power state parameters,
> >   in particular in preparation for PSCI OSI support
> > - Remove generic CPUidle operations infrastructure from the kernel
> >
> > This patchset does not go as far as removing the generic ARM CPUidle
> > infrastructure in order to collect feedback on the new approach
> > before completing the removal from the kernel, the generic and PSCI
> > CPUidle driver are left to co-exist.
> 
> I like the approach and I think this series definitely moves things in
> the right direction.
> 
> Of course, some additional cleanups/re-works on top are needed to show
> its full benefit, but step by step we reach that point.

I pushed code out as we agreed.

git://git.kernel.org/pub/scm/linux/kernel/git/lpieralisi/linux.git

branch: cpuidle/psci-driver

I will version the code as I update the patches, I will leave
them on the list for this week before sending a v2.

> > Tested on Juno platform with both DT and ACPI boot firmwares.
> >
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Ulf Hansson <ulf.hansson@...aro.org>
> > Cc: Sudeep Holla <sudeep.holla@....com>
> > Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> >
> > Lorenzo Pieralisi (6):
> >   ARM: cpuidle: Remove useless header include
> >   ARM: cpuidle: Remove overzealous error logging
> >   drivers: firmware: psci: Decouple checker from generic ARM CPUidle
> >   ARM: psci: cpuidle: Introduce PSCI CPUidle driver
> >   ARM: psci: cpuidle: Enable PSCI CPUidle driver
> >   PSCI: cpuidle: Refactor CPU suspend power_state parameter handling
> >
> >  MAINTAINERS                          |   8 +
> >  arch/arm/configs/imx_v6_v7_defconfig |   1 +
> >  arch/arm64/configs/defconfig         |   1 +
> >  arch/arm64/kernel/cpuidle.c          |  50 +++++-
> >  arch/arm64/kernel/psci.c             |   4 -
> >  drivers/cpuidle/Kconfig.arm          |   7 +
> >  drivers/cpuidle/Makefile             |   1 +
> >  drivers/cpuidle/cpuidle-arm.c        |  13 +-
> >  drivers/cpuidle/cpuidle-psci.c       | 235 +++++++++++++++++++++++++++
> >  drivers/firmware/psci/psci.c         | 167 +------------------
> >  drivers/firmware/psci/psci_checker.c |  16 +-
> >  include/linux/cpuidle.h              |  17 +-
> >  include/linux/psci.h                 |   4 +-
> >  13 files changed, 338 insertions(+), 186 deletions(-)
> >  create mode 100644 drivers/cpuidle/cpuidle-psci.c
> >
> > --
> > 2.21.0
> >
> 
> For the series, besides the minor comments I had on patch 4, feel free to add:
> 
> Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>

Thanks !
Lorenzo