linux-kernel - Re: [PATCH v9 05/11] of: base: Add of_get_cpu_state

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Date:   Wed, 10 Oct 2018 16:03:31 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-pm@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
        Kevin Hilman <khilman@...nel.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v9 05/11] of: base: Add of_get_cpu_state_node() to get
 idle states for a CPU node

On Wed, Oct 03, 2018 at 04:38:18PM +0200, Ulf Hansson wrote:
> The CPU's idle state nodes are currently parsed at the common cpuidle DT
> library, but also when initializing back-end data for the arch specific CPU
> operations, as in the PSCI driver case.
> 
> To avoid open-coding, let's introduce of_get_cpu_state_node(), which takes
> the device node for the CPU and the index to the requested idle state node,
> as in-parameters. In case a corresponding idle state node is found, it
> returns the node with the refcount incremented for it, else it returns
> NULL.
> 
> Moreover, for ARM, there are two generic methods, to describe the CPU's
> idle states, either via the flattened description through the
> "cpu-idle-states" binding [1] or via the hierarchical layout, using the
> "power-domains" and the "domain-idle-states" bindings [2]. Hence, let's
> take both options into account.
> 
> [1]
> Documentation/devicetree/bindings/arm/idle-states.txt
> [2]
> Documentation/devicetree/bindings/arm/psci.txt
> 
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: devicetree@...r.kernel.org
> Cc: Lina Iyer <ilina@...eaurora.org>
> Suggested-by: Sudeep Holla <sudeep.holla@....com>
> Co-developed-by: Lina Iyer <lina.iyer@...aro.org>
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> Reviewed-by: Rob Herring <robh@...nel.org>
> ---
>  drivers/of/base.c  | 35 +++++++++++++++++++++++++++++++++++
>  include/linux/of.h |  8 ++++++++
>  2 files changed, 43 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 74eaedd5b860..bf1d5fa34899 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -424,6 +424,41 @@ int of_cpu_node_to_id(struct device_node *cpu_node)
>  }
>  EXPORT_SYMBOL(of_cpu_node_to_id);
>  
> +/**
> + * of_get_cpu_state_node - Get CPU's idle state node at the given index
> + *
> + * @cpu_node: The device node for the CPU
> + * @index: The index in the list of the idle states
> + *
> + * Two generic methods can be used to describe a CPU's idle states, either via
> + * a flattened description through the "cpu-idle-states" binding or via the
> + * hierarchical layout, using the "power-domains" and the "domain-idle-states"
> + * bindings. This function check for both and returns the idle state node for
> + * the requested index.
> + *
> + * In case and idle state node is found at index, the refcount incremented for
> + * it, so call of_node_put() on it when done. Returns NULL if not found.
> + */
> +struct device_node *of_get_cpu_state_node(struct device_node *cpu_node,

No strong opinion but I am wondering if it makes sense to get cpu
logical index and fetch the cpu of_node here to contain the refcount on
it within this function while we are trying to consolidate. I do see
that may not be so useful in psci.c but keeping refcount for cpu of_node
here keeps the user free from that.

I am fine as it is if there are reasons not to do that.

--
Regards,
Sudeep