Re: [PATCH v8] clk: Add (devm_)clk_get_optional() functions

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

On Fri, Nov 30, 2018 at 10:25:37AM +0000, Phil Edworthy wrote:
> Hi Stephen,
> 
> On 30 November 2018 09:09 Stephen Boyd wrote:
> > Quoting Phil Edworthy (2018-11-20 06:14:45)
> > > This adds clk_get_optional() and devm_clk_get_optional() functions to
> > > get optional clocks.
> > > They behave the same as (devm_)clk_get except where there is no clock
> > > producer. In this case, instead of returning -ENOENT, the function
> > > returns NULL. This makes error checking simpler and allows
> > > clk_prepare_enable, etc to be called on the returned reference without
> > > additional checks.
> > 
> > Ok. I guess that works by virtue of how -ENOENT is returned by various
> > functions that are called deeper in the clk_get() path? I'm cautiously
> > optimistic. So cautious, we should probably add a comment to these optional
> > functions that indicate they rely on the functions they call to return -ENOENT
> > under the various conditions that make a clk optional.
> Yes, it does indeed rely on how clk_get() is implemented.
> Specifically, that if __of_clk_get_by_name() returns -EINVAL, the error is
> superseded by clk_get_sys() returning -ENOENT.
> As you say, a comment may help here.

Each time the question of the optional clk_get() stuff comes up, we go
around the same discussions time and time again.  So far, each time
has ended up flopping.

Yes, clk_get() can only ever return -ENOENT if it falls back to the
non-DT methods, because it assumes that the clk tables are complete
(it can do nothing else.)

I don't think it needs a comment because it's obvious from the code
and also from the implementation point of view.

> > > +static inline struct clk *clk_get_optional(struct device *dev, const
> > > +char *id)
> > 
> > Any kernel doc for this function?
> I took my cue from the surrounding functions, let me know if I have to add it.

I don't see you need to - this is an internal function by way of the
"static inline" you have before it.  It's not an API function.

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