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

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Date:	Wed, 27 Mar 2013 15:25:24 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	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 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 :)

--
viresh
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