Re: [PATCH 10/13] cpuidle: psci: Add a helper to attach a CPU to its PM domain

[Sudeep Holla <sudeep.holla@arm.com>]

On Thu, Oct 10, 2019 at 01:39:34PM +0200, 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.
> 
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
>  drivers/cpuidle/cpuidle-psci-domain.c | 21 +++++++++++++++++++++
>  drivers/cpuidle/cpuidle-psci.h        |  6 ++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
> index 3f5143ccc3e0..7429fd7626a1 100644
> --- a/drivers/cpuidle/cpuidle-psci-domain.c
> +++ b/drivers/cpuidle/cpuidle-psci-domain.c
> @@ -9,9 +9,11 @@
>  
>  #define pr_fmt(fmt) "CPUidle PSCI: " fmt
>  
> +#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 <linux/slab.h>
>  #include <linux/string.h>
> @@ -279,3 +281,22 @@ static int __init psci_idle_init_domains(void)
>  	return ret;
>  }
>  subsys_initcall(psci_idle_init_domains);
> +
> +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");

This clarifies the need for the fixed name. But why not just go by index 0
as the consumer of these psci power-domains will have only one power domain
entry. Why do we need this name compulsory ? Further, it's specified as
optional in the generic binding, do we make it "required" for this psci
idle states binding anywhere that I missed ?

--
Regards,
Sudeep