linux-kernel - Re: [PATCH V4] PM/OPP: discard duplicate OPPs

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Message-ID: <537B6663.30005@ti.com>
Date:	Tue, 20 May 2014 09:27:47 -0500
From:	Nishanth Menon <nm@...com>
To:	Viresh Kumar <viresh.kumar@...aro.org>, <rjw@...ysocki.net>
CC:	<linaro-kernel@...ts.linaro.org>, <linux-pm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <arvind.chauhan@....com>,
	<inderpal.s@...sung.com>, <chander.kashyap@...aro.org>,
	<pavel@....cz>, <len.brown@...el.com>,
	Chander Kashyap <k.chander@...sung.com>,
	Viresh Kumar <viresh.kumar@...rao.org>
Subject: Re: [PATCH V4] PM/OPP: discard duplicate OPPs

On 05/20/2014 09:17 AM, 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@...rao.org>
> ---
> V3->V4:
> - handle duplicate OPPs more appropriately
> - update comment over routine and enhance commit log
> 
> @Chander: I have kept your authorship as is, hope you don't mind me sending it
> on your behalf :)
> 
>  drivers/base/power/opp.c | 25 +++++++++++++++++++++++--
>  1 file changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index 2553867..cd9af42 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -389,6 +389,11 @@ EXPORT_SYMBOL_GPL(dev_pm_opp_find_freq_floor);
>   * The opp is made available by default and it can be controlled using
>   * dev_pm_opp_enable/disable functions.
>   *
> + * Duplicate OPPs are discarded. Will return 0 if new OPP was duplicate of
> + * existing one (i.e. same freq and volt) and -EEXIST would be returned if new
> + * OPP had same freq but different volt as of an existing OPP OR if both were
> + * same but earlier OPP was disabled.
How about we use the kernel-doc's "Return:"
Return: Returns 0 if new OPP was successfully added OR if the new OPP
was exact duplicate of existing one (i.e. same frequency and volt).
-EEXIST would be returned if new
OPP had same freq but different volt as of an existing OPP OR if both
were same but earlier OPP was disabled. -ENOMEM is returned if there
is no memory available to allocate requisite internal structures.

> + *
>   * Locking: The internal device_opp and opp structures are RCU protected.
>   * Hence this function internally uses RCU updater strategy with mutex locks
>   * to keep the integrity of the internal data structures. Callers should ensure
> @@ -443,15 +448,31 @@ 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;
> +
> +		pr_warn("%s: duplicate OPPs detected. Existing: freq: %lu, volt: %lu, enabled: %d. New: freq: %lu, volt: %lu, enabled: %d\n",
dev_warn please? we already know the dev pointer. Also can we reduce
this down to 80 character limit if possible?

> +			__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);
>  
> 

Otherwise, this looks fine to me.

-- 
Regards,
Nishanth Menon
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