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


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