[PATCH 04/10] clk: implement parent pass through functions

Sascha Hauer s.hauer at pengutronix.de
Tue Apr 19 13:53:18 EDT 2011

On Tue, Apr 19, 2011 at 10:20:28AM -0700, Stephen Boyd wrote:
> On 04/15/2011 12:08 PM, Sascha Hauer wrote:
> > A common case for clocks is that certain operations are not implemented
> > and shall be passed through to the parent. Add convenience functions
> > for this purpose
> >
> > Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
> > Cc: Jeremy Kerr <jeremy.kerr at canonical.com>
> >
> I was hoping we could just build the parent handling into the core
> instead of having every clk_ops->enable call the parent ops.
> Something like: if the clk_ops doesn't have a get_parent,
> clk_get_parent() would return NULL, and if the clk_ops doesn't have a
> set_parent, clk_set_parent() would do nothing.

That's the current behaviour (except that ERR_PTR(-ENOSYS) is returned
instead of NULL).

> Then clk_enable()/clk_disable() would call clk_get_parent() and then
> clk_enable() on that (whatever it is) before calling down into the
> ops->enable() function. Of course this means NULL is now the "no parent"
> value as opposed to ERR_PTR(-ENOSYS) but I'm willing to live with that
> since it makes things a bit simpler when you only have to check for NULL
> in the clk_enable()/clk_disable() path as opposed to NULL and IS_ERR.
> I'm afraid this patch means every time the clk_ops wants to enable its
> parent (which is almost always the case), it has to do so explicitly
> when we really just want to concentrate on what enabling means for that
> clock (namely setting some bits in some registers). Thoughts?

+1 for letting the core enable/disable and prepare/unprepare the parent
clocks. I scanned the different arm clock implementations and they all
do it, except the ones which do not implement parents at all.


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