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

From: Sudeep Holla <[email-masked]>
Date: Fri, 15 Nov 2019 17:13:36 +0000

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 <[email-masked]>
> ---
>
> 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 <[email-masked]>
> + *
> + */
> +
> +#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.

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

--
Regards,
Sudeep

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