Re: [PATCH v2 08/13] cpuidle: psci: Add a helper to attach a CPU to its PM domain

[Ulf Hansson <ulf.hansson@linaro.org>]

On Fri, 15 Nov 2019 at 18:13, Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> On Tue, Oct 29, 2019 at 05:44:33PM +0100, Ulf Hansson wrote:
> > Introduce a PSCI DT helper function, psci_dt_attach_cpu(), which takes a
> > CPU number as an in-parameter and tries to attach the CPU's struct device
> > to its corresponding PM domain.
> >
> > Let's makes use of dev_pm_domain_attach_by_name(), as it allows us to
> > specify "psci" as the "name" of the PM domain to attach to. Additionally,
> > let's also prepare the attached device to be power managed via runtime PM.
> >
> > Note that, the implementation of the new helper function is in a new
> > separate c-file, which may seems a bit too much at this point. However,
> > subsequent changes that implements the remaining part of the PM domain
> > support for cpuidle-psci, helps to justify this split.
> >
> > Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> > ---
> >
> > Changes in v2:
> >       - Reorder patch to be the first one that starts adding the PM domain
> >         support.
> >       - Rebased.
> >
> > ---
> >  drivers/cpuidle/Makefile              |  4 ++-
> >  drivers/cpuidle/cpuidle-psci-domain.c | 36 +++++++++++++++++++++++++++
> >  drivers/cpuidle/cpuidle-psci.h        | 12 +++++++++
> >  3 files changed, 51 insertions(+), 1 deletion(-)
> >  create mode 100644 drivers/cpuidle/cpuidle-psci-domain.c
> >  create mode 100644 drivers/cpuidle/cpuidle-psci.h
> >
> > diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
> > index ee70d5cc5b99..cc8c769d7fa9 100644
> > --- a/drivers/cpuidle/Makefile
> > +++ b/drivers/cpuidle/Makefile
> > @@ -21,7 +21,9 @@ obj-$(CONFIG_ARM_U8500_CPUIDLE)         += cpuidle-ux500.o
> >  obj-$(CONFIG_ARM_AT91_CPUIDLE)          += cpuidle-at91.o
> >  obj-$(CONFIG_ARM_EXYNOS_CPUIDLE)        += cpuidle-exynos.o
> >  obj-$(CONFIG_ARM_CPUIDLE)            += cpuidle-arm.o
> > -obj-$(CONFIG_ARM_PSCI_CPUIDLE)               += cpuidle-psci.o
> > +obj-$(CONFIG_ARM_PSCI_CPUIDLE)               += cpuidle_psci.o
> > +cpuidle_psci-y                               := cpuidle-psci.o
> > +cpuidle_psci-$(CONFIG_PM_GENERIC_DOMAINS_OF) += cpuidle-psci-domain.o
>
> This was super confusing for a minute until I noticed the difference
> between _ and - used here. I know such pattern is used in the kernel,
> just that it's difficult to notice on first go :)
>
> >
> >  ###############################################################################
> >  # MIPS drivers
> > diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
> > new file mode 100644
> > index 000000000000..bc7df4dc0686
> > --- /dev/null
> > +++ b/drivers/cpuidle/cpuidle-psci-domain.c
> > @@ -0,0 +1,36 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * PM domains for CPUs via genpd - managed by cpuidle-psci.
> > + *
> > + * Copyright (C) 2019 Linaro Ltd.
> > + * Author: Ulf Hansson <ulf.hansson@linaro.org>
> > + *
> > + */
> > +
> > +#include <linux/cpu.h>
> > +#include <linux/device.h>
> > +#include <linux/kernel.h>
> > +#include <linux/pm_domain.h>
> > +#include <linux/pm_runtime.h>
> > +#include <linux/psci.h>
> > +
> > +#include "cpuidle-psci.h"
> > +
> > +struct device *psci_dt_attach_cpu(int cpu)
> > +{
> > +     struct device *dev;
> > +
> > +     /* Currently limit the hierarchical topology to be used in OSI mode. */
> > +     if (!psci_has_osi_support())
> > +             return NULL;
> > +
> > +     dev = dev_pm_domain_attach_by_name(get_cpu_device(cpu), "psci");
> > +     if (IS_ERR_OR_NULL(dev))
> > +             return dev;
> > +
> > +     pm_runtime_irq_safe(dev);
> > +     if (cpu_online(cpu))
> > +             pm_runtime_get_sync(dev);
>
> I probably have to wait till I see the user of this, but until then I
> assume we have some way to deal with CPU HP machinery for this.

Yes, I discussed this with Lorenzo at LPC as well. I did not include a
patch in the series using a CPU HP, simply because I am targeting to
land the basic support first.

For now, this means that the "cluster" will remain on even if there
are CPUs being put offline.

>
> Other than that, it looks fine. I will get back to this to ack or with
> more questions as I review further.

Great, thanks!

Kind regards
Uffe