[RFC, PATCH 3/3] clk: add warnings for incorrect enable/prepare semantics

Hi Uwe,

This implies the warning is only issued on clocks that have a prepare
callback.  If we want to enforce the new API the warning here shouldn't
depend on clk->ops->prepare.  (clk_prepare and clk_unprepare need to
be changed then to adapt the prepare_count even in the absence of
clk->ops->prepare.)

Yeah, it's a decision about either adding a small cost to all clk_prepare()s 
(ie, adding cost when there is no prepare callback), or checking for the 
correct prepare/enable semantics for all clocks (even when it doesn't matter 
for that particular clock). I chose the first as more important, but happy to 
go either way here.

Cheers,


Jeremy