Locking in the clk API

Jeremy Kerr jeremy.kerr at canonical.com
Tue Jan 11 04:44:59 EST 2011

Hi Russell,

> I object to this as one of the purposes behind the clk API is to allow
> power savings to be made, and unless we can perform clk enable/disable
> from atomic contexts, the best you can do is enable the clock when the
> device is probed and disable it when it's released.
> [...]
> Sometimes the only point that you know you need the clock enabled is when
> your driver has already been called in an atomic context.

.. provided that the enable (and subsequent things that depend on the clock 
signal to be valid) can't be deferred; I'm not sure how often this will be 

So, it sounds like the best approach is to provide an atomic clk_enable. I 
agree with Sascha that the clk_enable and clk_enable_atomic polarity makes the 
most sense, so how about:

int clk_enable(struct clk *clk)


int clk_enable_atomic(struct clk *clk)
	BUG_ON(!(clk->flags & CLK_ATOMIC));


Paul: even though you mention that the atomic clocks are the usual case, I 
think that this way around illustrates the atomic 'restriction' at the call 
site more clearly. When the drivers don't care about the atomicity, 
clk_enable() is fine. When drivers do need an atomic clock, 
clk_enable_atomic() shows this requirement.



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