Date:	Mon, 19 May 2014 13:34:17 -0500
From:	Nishanth Menon <nm@...com>
To:	Inderpal Singh <inderpal.s@...sung.com>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH] PM / OPP: Implement free_opp_table function

On Mon, May 19, 2014 at 1:08 PM, Inderpal Singh <inderpal.s@...sung.com> wrote:
> Hi Nishanth,
>
> Thanks for the review comments.
>
> On Mon, May 19, 2014 at 6:43 PM, Nishanth Menon <nm@...com> wrote:
>> On 05/16/2014 04:09 AM, Inderpal Singh wrote:
>>> At the driver unloading time the associated opp table may need
>>> to be deleted. Otherwise it amounts to memory leak. The existing
>>> OPP library does not have provison to do so.
>>>
>>> Hence this patch implements the function to free the opp table.
>>>
>>> Signed-off-by: Inderpal Singh <inderpal.s@...sung.com>
>>> ---
>>>  drivers/base/power/opp.c | 41 +++++++++++++++++++++++++++++++++++++++++
>>>  include/linux/pm_opp.h   |  6 ++++++
>>>  2 files changed, 47 insertions(+)
>>>
>>> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
>>> index d9e376a..d45ffd5 100644
>>> --- a/drivers/base/power/opp.c
>>> +++ b/drivers/base/power/opp.c
>>> @@ -654,4 +654,45 @@ int of_init_opp_table(struct device *dev)
>>>       return 0;
>>>  }
>>>  EXPORT_SYMBOL_GPL(of_init_opp_table);
>>> +
>>> +/**
>>> + * dev_pm_opp_free_opp_table() - free the opp table
>>> + * @dev:     device for which we do this operation
>>> + *
>>> + * Free up the allocated opp table
>>> + *
>>> + * 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
>>> + * that this function is *NOT* called under RCU protection or in contexts where
>>> + * mutex locking or synchronize_rcu() blocking calls cannot be used.
>>> + */
>>> +void dev_pm_opp_free_opp_table(struct device *dev)
>>> +{
>>> +     struct device_opp *dev_opp = NULL;
>>> +     struct dev_pm_opp *opp;
>>> +
>> if (!dev)
>>         return;
>>
>
> missed it. Will take care in the next version.
>
>>> +     /* Hold our list modification lock here */
>>> +     mutex_lock(&dev_opp_list_lock);
>>> +
>>> +     /* Check for existing list for 'dev' */
>>> +     dev_opp = find_device_opp(dev);
>>> +     if (IS_ERR(dev_opp)) {
>>> +             mutex_unlock(&dev_opp_list_lock);
>>> +             return;
>>> +     }
>>> +
>>> +     while (!list_empty(&dev_opp->opp_list)) {
>>> +             opp = list_entry_rcu(dev_opp->opp_list.next,
>>> +                                     struct dev_pm_opp, node);
>>> +             list_del_rcu(&opp->node);
>>> +             kfree_rcu(opp, head);
>>> +     }
>>
>> How about the OPP notifiers? should'nt we add a new event
>> OPP_EVENT_REMOVE?
>>
>
> As this function is to free the whole opp table. Hence, I think,
> notifier may not be needed. It may be required for per opp removal as
> is the case with opp addition and enable/disable. But at present there
> are no users of these notifiers at all. Let me know your view.

umm.. we do have devfreq which depends on OPPs :).

>> To maintain non-dt behavior coherency, should'nt we rather add a
>> opp_remove or an opp_del function?
>
> Yes we should have opp_remove as well, but what's the use case ?
> Should we go ahead and implement it Or, wait for the use-case?

IMHO, if we are doing it properly, we should add the requisite
function as well. we dont want to have differing behavior device tree
Vs non-DT.

Regards,
Nishanth Menon
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