Messages in this thread |  | | Date | Mon, 24 Feb 2014 21:30:05 -0300 | From | Emilio López <> | Subject | Re: [PATCH 1/5] clk: sun6i: Protect CPU clock |
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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: >> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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