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

[Nicolas Pitre]

On Mon, 7 Feb 2011, Jeremy Kerr wrote:

> 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.

The prepare method being called from non-atomic context cannot be 
considered to be in a speed critical path.  Most of the time, this is 
going to be called on driver initialization or the like, and that's a 
relatively rare event. Therefore this really small cost to clk_prepare() 
is definitively worth it to help proper usage of the API.  If this ever 
becomes a problem then this could be confined to some CONFIG_CLK_DEBUG 
or the like.  But when introducing a new API it is best to be more 
strict to help people get its usage right (without going overboard with 
it of course).


Nicolas