Hi Russell,

El 24/02/14 21:01, Russell King - ARM Linux escribió:

Hi Emilio.

On Mon, Feb 24, 2014 at 08:38:44PM -0300, Emilio López wrote:

quoted

Why is this so? Can't a clock be left enabled while nobody has a
reference to it? I have looked around in Documentation/ (rather quickly
I must say) and have not found any explicit mention that it is required
to keep a reference to the clock while it's enabled. I'd appreciate it
if you could explain this a bit more verbosely or point me to the
relevant documents.

First up, if you have a requirement that a clock be enabled, then is it
not unreasonable to ensure that the clock is referenced?

I was under the impression that the reference count was orthogonal to 
the clock status, but after getting that clarified, I can see your point.

Secondly, what if we have code which scans the clocks in the system,
shutting down those leaf clocks which appear to be unreferenced?

Indeed, that would break things.

Thirdly, the API (as I designed it) says so:

/**
  * clk_put      - "free" the clock source
  * @clk: clock source
  *
  * Note: drivers must ensure that all clk_enable calls made on this
  * clock source are balanced by clk_disable calls prior to calling
  * this function.
  *
  * clk_put should not be called from within interrupt context.
  */
void clk_put(struct clk *clk);

which has been there since the API was first created - it's part of the
contract between drivers using the API and implementers creating something
which conforms to the API - which today means CCF.

That's enough of a reason on its own :) I should have checked clk.h

The intention here is that while there are any users holding a clk_get()
reference on a clock, the clock is assumed to be required for some
device, and the struct clk may not be kfree'd, nor may its state be
changed in an unpredictable way to those drivers holding a reference
to it.

I understand now, thanks for the insight. I'll talk with Maxime and get 
this sorted out.

As a side note, should drivers/base/power/clock_ops.c be fixed too? I 
have added Rafael to Cc.

Cheers,

Emilio

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