linux-kernel - Re: [PATCH v4] clk: allow reentrant calls into the clk framework

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Date:	Wed, 27 Mar 2013 11:03:21 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Mike Turquette <mturquette@...aro.org>,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	linux-kernel@...r.kernel.org,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	David Brown <davidb@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4] clk: allow reentrant calls into the clk framework

On 27 March 2013 10:55, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 27 March 2013 15:10, Thomas Gleixner <tglx@...utronix.de> wrote:
>> On Wed, 27 Mar 2013, Mike Turquette wrote:
>>
>>> Reentrancy into the clock framework from the clk.h api is necessary
>>> for clocks that are prepared and unprepared via i2c_transfer (which
>>> includes many PMICs and discrete audio chips) as well as for several
>>> other use cases.
>>
>> That explanation sucks.
>>
>> Why does an i2c clock need reentrancy? Just because it's i2c or what?
>
> I am noway connected to this development but was just going through
> your mail and i think i might know the answer why is this required.
>
> Consider an example where an external chip has clock controller and has
> bits which can be programmed to enable/disable clock. And this chip is
> connected via spi/i2c to SoC.
>
> clk_prepare(peripheral on external chip)
>   -> i2c_xfer(to write to external chips register)
>       -> clk_enable(i2c controller)
>           ->controller-xfer-routine.. and finally we enable clk here...
>
>
> Sorry if i am on the wrong side :)

I agree with you Viresh. I guess Mike should update the commit message.

I would also like add another reason to why this is needed. For some
clks you would like to do pinctrl operations from a clk hw. But since
a pinctrl driver likely requires a clk to be prepared|enabled, we run
into a clk reentrant issue.

Kind regards
Ulf Hansson

>
> --
> viresh
> --
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