linux-kernel - Re: [PATCH 2/2] clk: allow reentrant calls into the clk framework

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Message-ID: <CAPtuhTiPqJkQw-nJMuyaZuTQ2iYbrbtEWMobBf5fWCB3dUG2jQ@mail.gmail.com>
Date:	Thu, 28 Mar 2013 08:23:22 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Patch Tracking <patches@...aro.org>,
	linaro-kernel@...ts.linaro.org,
	Rajagopal Venkat <rajagopal.venkat@...aro.org>,
	David Brown <davidb@...eaurora.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	laurent.pinchart@...asonboard.com
Subject: Re: [PATCH 2/2] clk: allow reentrant calls into the clk framework

On Thu, Mar 28, 2013 at 2:33 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Wed, 27 Mar 2013, Mike Turquette wrote:
>
>> Reentrancy into the clock framework is necessary for clock operations
>> that result in nested calls to the clk api.  A common example is a clock
>> that is prepared via an i2c transaction, such as a clock inside of a
>> discrete audio chip or a power management IC.  The i2c subsystem itself
>> will use the clk api resulting in a deadlock:
>>
>> clk_prepare(audio_clk)
>>       i2c_transfer(..)
>>               clk_prepare(i2c_controller_clk)
>>
>> The ability to reenter the clock framework prevents this deadlock.
>>
>> Other use cases exist such as allowing .set_rate callbacks to call
>> clk_set_parent to achieve the best rate, or to save power in certain
>> configurations.  Yet another example is performing pinctrl operations
>> from a clk_ops callback.  Calls into the pinctrl subsystem may call
>> clk_{un}prepare on an unrelated clock.  Allowing for nested calls to
>> reenter the clock framework enables both of these use cases.
>>
>> Reentrancy is implemented by two global pointers that track the owner
>> currently holding a global lock.  One pointer tracks the owner during
>> sleepable, mutex-protected operations and the other one tracks the owner
>> during non-interruptible, spinlock-protected operations.
>>
>> When the clk framework is entered we try to hold the global lock.  If it
>> is held we compare the current task id against the current owner; a
>
> s/task id/task/ We store a the task pointer in the owner variable.
>
> Reviewed-by: Thomas Gleixner <tglx@...utronix.de>

Will fix the typo and add your reviewed-by.

Thanks for the review,
Mike
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