linux-kernel - Re: cpuidle/powernv: Read target_residency value of idle states from DT if available

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Message-Id: <20150120054506.F13591402E0@ozlabs.org>
Date:	Tue, 20 Jan 2015 16:45:06 +1100 (AEDT)
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	rafael.j.wysocki@...el.com
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: cpuidle/powernv: Read target_residency value of idle states from DT if available

On Mon, 2015-19-01 at 11:32:51 UTC, Preeti U Murthy wrote:
> The device tree now exposes the residency values for different idle states. Read
> these values instead of calculating residency from the latency values. The values
> exposed in the DT are validated for optimal power efficiency. However to maintain
> compatibility with the older firmware code which does not expose residency
> values, use default values as a fallback mechanism. While at it, clump
> the common parts of device tree parsing into one chunk.
> 
> Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
> ---
> 
>  drivers/cpuidle/cpuidle-powernv.c |   39 ++++++++++++++++++++++++-------------
>  1 file changed, 25 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
> index 2726663..9e732e1 100644
> --- a/drivers/cpuidle/cpuidle-powernv.c
> +++ b/drivers/cpuidle/cpuidle-powernv.c
> @@ -162,7 +162,8 @@ static int powernv_add_idle_states(void)
>  	int dt_idle_states;
>  	const __be32 *idle_state_flags;
>  	const __be32 *idle_state_latency;
> -	u32 len_flags, flags, latency_ns;
> +	const __be32 *idle_state_residency;
> +	u32 len_flags, flags, latency_ns, residency_ns;
>  	int i;
>  
>  	/* Currently we have snooze statically defined */
> @@ -186,14 +187,21 @@ static int powernv_add_idle_states(void)
>  		return nr_idle_states;
>  	}
>  
> +	idle_state_residency = of_get_property(power_mgt,
> +			"ibm,cpu-idle-state-residency-ns", NULL);
> +	if (!idle_state_residency) {
> +		pr_warn("DT-PowerMgmt: missing ibm,cpu-idle-state-residency-ns\n");
> +		pr_warn("Falling back to default values\n");
> +	}

This would be better done with something like:

	rc = of_read_property_u32(power_mgt, "ibm,cpu-idle-state-residency-ns", &residency_ns);
	if (!rc) {
		pr_info("cpuidle-powernv: missing ibm,cpu-idle-state-residency-ns\n");
		residency_ns = 300000;
	}

cheers
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