linux-kernel - Re: [PATCH V5] PM/OPP: discard duplicate OPPs

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Message-ID: <1555967.8fxByr2j83@vostro.rjw.lan>
Date:	Tue, 20 May 2014 23:09:47 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, arvind.chauhan@....com,
	inderpal.s@...sung.com, nm@...com, chander.kashyap@...aro.org,
	pavel@....cz, len.brown@...el.com,
	Chander Kashyap <k.chander@...sung.com>
Subject: Re: [PATCH V5] PM/OPP: discard duplicate OPPs

On Tuesday, May 20, 2014 08:23:28 PM Viresh Kumar wrote:
> From: Chander Kashyap <k.chander@...sung.com>
> 
> We don't have any protection against addition of duplicate OPPs currently and
> in case some code tries to add them it will end up corrupting OPP tables.
> 
> There can be many combinations in which we may end up trying duplicate OPPs:
> - both freq and volt are same, but earlier OPP may or may not be active.
> - only freq is same and volt is different.
> 
> This patch tries to implement below logic for these cases:
> 
> Return 0 if new OPP was duplicate of existing one (i.e. same freq and volt) and
> return -EEXIST if new OPP had same freq but different volt as of an existing OPP
> OR if both freq/volt were same but earlier OPP was disabled.
> 
> Signed-off-by: Chander Kashyap <k.chander@...sung.com>
> Signed-off-by: Inderpal Singh <inderpal.s@...sung.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> V4->V5:
> - Mention Return values under 'Return:' clause of doc style comment.
> - s/pr_warn/dev_warn
> - s/linrao/linaro in my email id :(
> 
>  drivers/base/power/opp.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index 2553867..6a06d43 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -394,6 +394,13 @@ EXPORT_SYMBOL_GPL(dev_pm_opp_find_freq_floor);
>   * to keep the integrity of the internal data structures. Callers should ensure
>   * that this function is *NOT* called under RCU protection or in contexts where
>   * mutex cannot be locked.
> + *
> + * Returns:
> + * 0:		On success OR
> + *		Duplicate OPPs (both freq and volt are same) and opp->available
> + * -EEXIST:	Freq are same and volt are different OR
> + *		Duplicate OPPs (both freq and volt are same) and !opp->available
> + * -ENOMEM:	Memory allocation failure
>   */
>  int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
>  {
> @@ -443,15 +450,31 @@ int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
>  	new_opp->u_volt = u_volt;
>  	new_opp->available = true;
>  
> -	/* Insert new OPP in order of increasing frequency */
> +	/*
> +	 * Insert new OPP in order of increasing frequency
> +	 * and discard if already present
> +	 */
>  	head = &dev_opp->opp_list;
>  	list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
> -		if (new_opp->rate < opp->rate)
> +		if (new_opp->rate <= opp->rate)
>  			break;
>  		else
>  			head = &opp->node;
>  	}
>  
> +	/* Duplicate OPPs ? */
> +	if (new_opp->rate == opp->rate) {
> +		int ret = (new_opp->u_volt == opp->u_volt) && opp->available ?
> +			0 : -EEXIST;

The parens are not necessary.  And is the direction correct?

> +
> +		dev_warn(dev, "%s: duplicate OPPs detected. Existing: freq: %lu, volt: %lu, enabled: %d. New: freq: %lu, volt: %lu, enabled: %d\n",
> +			__func__, opp->rate, opp->u_volt, opp->available,
> +			new_opp->rate, new_opp->u_volt, new_opp->available);
> +		mutex_unlock(&dev_opp_list_lock);
> +		kfree(new_opp);
> +		return ret;
> +	}
> +
>  	list_add_rcu(&new_opp->node, head);
>  	mutex_unlock(&dev_opp_list_lock);
>  
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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