linux-kernel - Re: [PATCH v3 1/5] PM / clock_ops: Add pm_clk_add

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Date:	Thu, 23 Oct 2014 21:04:19 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	<ssantosh@...nel.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>,
	<khilman@...aro.org>, <linux-pm@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>, <grant.likely@...retlab.ca>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v3 1/5] PM / clock_ops: Add pm_clk_add_clk()

On 10/23/2014 08:13 PM, Dmitry Torokhov wrote:
> On Thu, Oct 23, 2014 at 07:18:49PM +0300, Grygorii Strashko wrote:
>> On 10/23/2014 06:49 PM, Dmitry Torokhov wrote:
>>> On Thu, Oct 23, 2014 at 05:22:58PM +0300, Grygorii Strashko wrote:
>>>> From: Geert Uytterhoeven <geert+renesas@...der.be>
>>>>
>>>> The existing pm_clk_add() allows to pass a clock by con_id. However,
>>>> when referring to a specific clock from DT, no con_id is available.
>>>>
>>>> Add pm_clk_add_clk(), which allows to specify the struct clk * directly.
>>>>
>>>> CC: Ulf Hansson <ulf.hansson@...aro.org>
>>>> CC: Dmitry Torokhov <dmitry.torokhov@...il.com>
>>>> Reviewed-by: Santosh Shilimkar <santosh.shilimkar@...com>
>>>> Reviewed-by: Kevin Hilman <khilman@...aro.org>
>>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
>>>> ---
>>>>   drivers/base/power/clock_ops.c | 41 +++++++++++++++++++++++++++++++----------
>>>>   include/linux/pm_clock.h       |  8 ++++++++
>>>>   2 files changed, 39 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/base/power/clock_ops.c b/drivers/base/power/clock_ops.c
>>>> index 7836930..f14b767 100644
>>>> --- a/drivers/base/power/clock_ops.c
>>>> +++ b/drivers/base/power/clock_ops.c
>>>> @@ -53,7 +53,8 @@ static inline int __pm_clk_enable(struct device *dev, struct clk *clk)
>>>>    */
>>>>   static void pm_clk_acquire(struct device *dev, struct pm_clock_entry *ce)
>>>>   {
>>>> -	ce->clk = clk_get(dev, ce->con_id);
>>>> +	if (!ce->clk)
>>>> +		ce->clk = clk_get(dev, ce->con_id);
>>>>   	if (IS_ERR(ce->clk)) {
>>>>   		ce->status = PCE_STATUS_ERROR;
>>>>   	} else {
>>>> @@ -63,15 +64,8 @@ static void pm_clk_acquire(struct device *dev, struct pm_clock_entry *ce)
>>>>   	}
>>>>   }
>>>>
>>>> -/**
>>>> - * pm_clk_add - Start using a device clock for power management.
>>>> - * @dev: Device whose clock is going to be used for power management.
>>>> - * @con_id: Connection ID of the clock.
>>>> - *
>>>> - * Add the clock represented by @con_id to the list of clocks used for
>>>> - * the power management of @dev.
>>>> - */
>>>> -int pm_clk_add(struct device *dev, const char *con_id)
>>>> +static int __pm_clk_add(struct device *dev, const char *con_id,
>>>> +			struct clk *clk)
>>>>   {
>>>>   	struct pm_subsys_data *psd = dev_to_psd(dev);
>>>>   	struct pm_clock_entry *ce;
>>>> @@ -93,6 +87,8 @@ int pm_clk_add(struct device *dev, const char *con_id)
>>>>   			kfree(ce);
>>>>   			return -ENOMEM;
>>>>   		}
>>>> +	} else {
>>>
>>> You need __clk_get(clk) here, otherwise when you will be removing clocks
>>> you'll be dropping a reference that does not belong to you (as yiou have
>>> not taken it).
>>
>> No, I don't ;)
>>
>> pm_clk_add_clk is intended to be used with valid pointer on clk,
>> which means clk_get() has been called already. In our case:
>> 	clk = of_clk_get(dev->of_node, i));
>> 	ret = pm_clk_add_clk(dev, clk);
>>
>> It's just a different way to fill list of clocks for device,
>> once pm_clk_add_clk() is called - PM clock framework will be the owner
>> of clock.
>
> No, this is not how the rest of refcounted APIs work in the kernel. You
> do not take over other's references and if you need to store pointer to
> refcounted object you are responsible for taking your own reference. See
> how we work with device structures, OF nodes, etc, etc.
>
> The proper pattern here should be (unless the driver wants to hold on to
> the clock for its own purposes):
>
> 	clk = of_clk_get(dev->of_node, i));
> 	ret = pm_clk_add_clk(dev, clk);
> 	clk_put(clk);
>
> with pm_clk_add_clk() taking and managing _its own_ reference and the
> caller (driver) managing _its_ reference.
>
> So FWIW strong NAK here from me.

Ok. I'll update and resend.

regards,
-grygorii

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