Re: [PATCH v4 1/2] ARM: keystone: pm: switch to use generic pm domains

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Tue, Nov 25, 2014 at 03:30:20PM +0200, Grygorii Strashko wrote:
> On 11/25/2014 02:09 PM, Arnd Bergmann wrote:
> > It might be possible to do this implicitly if the driver calls clk_get(),
> > basically doing clk_get() (or another call if necessary) would prevent the
> > simple pmdomain from turning it off during suspend.
> 
> Unfortunately, clk_get() will not work, because drivers still need to use it
> to get functional clocks even if they are not going to control them explicitly.
> For example, if it need to know clock's rate.

If you don't want a clock to be turned off, then clk_get() it, then
clk_prepare() it, and finally clk_enable() it.

Even if someone else gets it, the only time that a clock is turned off
is when _all_ users of it mutually agree that it can be turned off - by
every user disabling (and possibly unpreparing) it.

So, if the PM domain code gets a clock, prepares and enables it, then
a driver gets the same clock, prepares and enables it also, it won't
be disabled until _both_ the PM domain code _and_ the driver disable
and unprepare the clock.

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