Re: [PATCH v9 05/11] of: base: Add of_get_cpu_state_node() to get idle states for a CPU node

From: Sudeep Holla <sudeep.holla@arm.com>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: "Rafael J . Wysocki" <rjw@rjwysocki.net>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	linux-pm@vger.kernel.org, Tony Lindgren <tony@atomide.com>,
	Kevin Hilman <khilman@kernel.org>,
	Lina Iyer <ilina@codeaurora.org>,
	Rob Herring <robh+dt@kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	linux-arm-kernel@lists.infradead.org,
	linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
	devicetree@vger.kernel.org, Sudeep Holla <sudeep.holla@arm.com>
Subject: Re: [PATCH v9 05/11] of: base: Add of_get_cpu_state_node() to get idle states for a CPU node
Date: Wed, 10 Oct 2018 16:03:31 +0100	[thread overview]
Message-ID: <20181010150331.GB4844@e107155-lin> (raw)
In-Reply-To: <20181003143824.13059-6-ulf.hansson@linaro.org>

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@kernel.org>
> Cc: devicetree@vger.kernel.org
> Cc: Lina Iyer <ilina@codeaurora.org>
> Suggested-by: Sudeep Holla <sudeep.holla@arm.com>
> Co-developed-by: Lina Iyer <lina.iyer@linaro.org>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> Reviewed-by: Rob Herring <robh@kernel.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