[RFC 1/1] clk: Add notifier support in clk_prepare_enable/clk_disable_unprepare

[Bill Huang]

On Tue, 2013-03-12 at 21:40 +0800, Russell King - ARM Linux wrote:
> On Tue, Mar 12, 2013 at 05:37:41AM -0700, Bill Huang wrote:
> > Add the below four notifier events so drivers which are interested in
> > knowing the clock status can act accordingly. This is extremely useful
> > in some of the DVFS (Dynamic Voltage Frequency Scaling) design.
> > 
> > PRE_CLK_ENABLE
> > POST_CLK_ENABLE
> > PRE_CLK_DISABLE
> > POST_CLK_DISABLE
> > 
> > Signed-off-by: Bill Huang <bilhuang at nvidia.com>
> 
> NAK.  *Sigh* NO, this is the wrong level to be doing stuff like this.
> 
> The *ONLY* thing that clk_prepare_enable() and clk_prepare_disable() should
> *EVER* be doing is calling clk_prepare(), clk_enable(), clk_disable() and
> clk_unprepare().  Those two functions are *merely* helpers for drivers
> who don't wish to make the individual calls.
> 
> Drivers are still completely free to call the individual functions, at
> which point your proposal breaks horribly - and they _do_ call the
> individual functions.
I'm proposing to give device driver a choice when it knows that some
driver might be interested in knowing its clock's enabled/disabled state
change at runtime, this is very important for centralized DVFS core
driver. It is not meant to be covering all cases especially for drivers
which is not part of the DVFS, so we don't care if it is calling
clk_enable/disable directly or not.

One major side effect being that it affects those existing drivers who
were calling clk_prepare_enable and clk_prepare_disable but it should
not hurt if they don't care the notifier, or maybe we should define a
new set of functions for the purpose?

Mike, how do you think? Thanks.