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

[Phil Edworthy <phil.edworthy@renesas.com>]

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superseded by clk_get_sys() returning -ENOENT.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.


> >
> > diff --git a/include/linux/clk.h b/include/linux/clk.h index
> > a7773b5c0b9f..3ea3c78f62dd 100644
> > --- a/include/linux/clk.h
> > +++ b/include/linux/clk.h
> > @@ -383,6 +383,17 @@ int __must_check devm_clk_bulk_get_all(struct
> device *dev,
> >   */
> >  struct clk *devm_clk_get(struct device *dev, const char *id);
> >
> > +/**
> > + * devm_clk_get_optional - lookup and obtain a managed reference to an
> optional
> > + *                        clock producer.
> > + * @dev: device for clock "consumer"
> > + * @id: clock consumer ID
> > + *
> > + * Behaves the same as devm_clk_get except where there is no clock
> > +producer. In
> 
> Please add () around devm_clk_get() so we know it's a function.
Will do.


> > + * this case, instead of returning -ENOENT, the function returns NULL.
> > + */
> > +struct clk *devm_clk_get_optional(struct device *dev, const char
> > +*id);
> > +
> >  /**
> >   * devm_get_clk_from_child - lookup and obtain a managed reference to a
> >   *                          clock producer from child node.
> > @@ -718,6 +729,12 @@ static inline struct clk *devm_clk_get(struct device
> *dev, const char *id)
> >         return NULL;
> >  }
> >
> > +static inline struct clk *devm_clk_get_optional(struct device *dev,
> > +                                               const char *id) {
> > +       return NULL;
> > +}
> > +
> >  static inline int __must_check devm_clk_bulk_get(struct device *dev, int
> num_clks,
> >                                                  struct clk_bulk_data
> > *clks)  { @@ -862,6 +879,16 @@ static inline void
> > clk_bulk_disable_unprepare(int num_clks,
> >         clk_bulk_unprepare(num_clks, clks);  }
> >
> > +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.

Thanks
Phil

> > +{
> > +       struct clk *clk = clk_get(dev, id);
> > +
> > +       if (clk == ERR_PTR(-ENOENT))
> > +               clk = NULL;
> > +
> > +       return clk;
> > +}
> > +