linux-kernel - Re: [PATCH v6 5/8] PM / devfreq: tegra: remove operating-points

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Message-id: <192647817.276191426656237193.JavaMail.weblogic@epmlwas07d>
Date:	Wed, 18 Mar 2015 05:24:00 +0000 (GMT)
From:	MyungJoo Ham <myungjoo.ham@...sung.com>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Cc:	Mikko Perttunen <mikko.perttunen@...si.fi>,
	박경민 <kyungmin.park@...sung.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 5/8] PM / devfreq: tegra: remove operating-points

> As the DT bindings don't have an operating-points property any more,
> build the OPP table from the frequencies supported by the EMC clock.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> ---
>  drivers/devfreq/tegra-devfreq.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/devfreq/tegra-devfreq.c b/drivers/devfreq/tegra-devfreq.c
> index 5a6164c..1de3f8b 100644
> --- a/drivers/devfreq/tegra-devfreq.c
> +++ b/drivers/devfreq/tegra-devfreq.c
> @@ -618,6 +618,7 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>  	struct tegra_devfreq_device *dev;
>  	struct resource *res;
>  	unsigned int i;
> +	unsigned long rate;
>  	int irq;
>  	int err;
>  
> @@ -649,12 +650,6 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>  		return PTR_ERR(tegra->emc_clock);
>  	}
>  
> -	err = of_init_opp_table(&pdev->dev);
> -	if (err) {
> -		dev_err(&pdev->dev, "Failed to init operating point table\n");
> -		return err;
> -	}
> -
>  	clk_set_rate(tegra->emc_clock, ULONG_MAX);
>  
>  	tegra->rate_change_nb.notifier_call = tegra_actmon_rate_notify_cb;
> @@ -691,6 +686,11 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>  		tegra_actmon_configure_device(tegra, dev);
>  	}
>  
> +	for (rate = 0; rate <= tegra->max_freq * KHZ; rate++) {
> +		rate = clk_round_rate(tegra->emc_clock, rate);
> +		dev_pm_opp_add(&pdev->dev, rate, 0);
> +	}
> +

Although I am not going to NACK for the single-time performance of a
single device driver for a device that I do not have or fully understand,
please note that you may be wasting several billion cycles unless
your product is running at MHZ/kHZ level.

What is going on with this loop? Do you really have such a virtually-continuous
frequency scaling in your product? (Wow.... but in such a case, I don't think
OPP is appropriate.)


Cheers,
MyungJoo


>  	irq = platform_get_irq(pdev, 0);
>  	if (irq <= 0) {
>  		dev_err(&pdev->dev, "Failed to get IRQ\n");
> -- 
> 2.1.0
>