linux-kernel - Re: [PATCH v2] PM / devfreq: Use freq_table for available

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Date:	Mon, 28 Apr 2014 01:41:55 +0000 (GMT)
From:	MyungJoo Ham <myungjoo.ham@...sung.com>
To:	Saravana Kannan <skannan@...eaurora.org>,
	박경민 <kyungmin.park@...sung.com>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] PM / devfreq: Use freq_table for available_frequencies

> Some devices use freq_table instead of OPP. For those devices, the
> available_frequencies file shows up empty. Fix that by using freq_table to
> generate the available_frequencies data when it's available.
> 
> OPP find frequency APIs also skips frequencies that have been temporarily
> disabled (say, due to thermal, etc). Since available_frequencies is
> supposed to show the entire list of available frequencies without taking
> temporary limits into consideration, preference is given to freq_table when
> available.
> 
> Signed-off-by: Saravana Kannan <skannan@...eaurora.org>
> ---
>  drivers/devfreq/devfreq.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 2042ec3..527cbe2 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -912,20 +912,27 @@ static ssize_t available_frequencies_show(struct device *d,
>  	struct devfreq *df = to_devfreq(d);
>  	struct device *dev = df->dev.parent;
>  	struct dev_pm_opp *opp;
> +	unsigned int i = 0;
>  	ssize_t count = 0;
>  	unsigned long freq = 0;
>  
> -	rcu_read_lock();
> -	do {
> -		opp = dev_pm_opp_find_freq_ceil(dev, &freq);
> -		if (IS_ERR(opp))
> -			break;
> -
> -		count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
> -				   "%lu ", freq);
> -		freq++;
> -	} while (1);
> -	rcu_read_unlock();
> +	if (df->profile->freq_table) {
> +		for (i = 0; i < df->profile->max_state; i++)
> +			count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
> +					   "%u ", df->profile->freq_table[i]);

You are hereby changing the semmantics of the original
available_frequencies node.

When a frequency/voltage pair has been disabled (opp_disable), probably
by opp_disable(), the frequency is no more "available".
However, when the driver author supplied freq_table as well as OPP
in order to see the statistics, the node will behave differently.

Please do not affect the current users as long as it does not give
additional benefit or fix a bug.


Cheers,
MyungJoo.


> +	} else {
> +		rcu_read_lock();
> +		do {
> +			opp = dev_pm_opp_find_freq_ceil(dev, &freq);
> +			if (IS_ERR(opp))
> +				break;
> +
> +			count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
> +					   "%lu ", freq);
> +			freq++;
> +		} while (1);
> +		rcu_read_unlock();
> +	}
>  
>  	/* Truncate the trailing space */
>  	if (count)
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> hosted by The Linux Foundation
>