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SubjectRe: [PATCH] mfd: syscon: Add syscon_regmap_lookup_by_phandle_optional() function.
I noticed that my earlier reply was rejected by some mail servers,
resending from @kernel.org to make sure everyone has it.

On Tue, Oct 27, 2020 at 10:57 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Tue, Oct 27, 2020 at 10:11 PM Enric Balletbo i Serra
> <enric.balletbo@collabora.com> wrote:
> >
> > This adds syscon_regmap_lookup_by_phandle_optional() function to get an
> > optional regmap.
> >
> > It behaves the same as syscon_regmap_lookup_by_phandle() except where
> > there is no regmap phandle. In this case, instead of returning -ENODEV,
> > the function returns NULL. This makes error checking simpler when the
> > regmap phandle is optional.
> >
> > Suggested-by: Nicolas Boichat <drinkcat@chromium.org>
> > Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
>
> Looks good in principle.
>
> > @@ -255,6 +255,19 @@ struct regmap *syscon_regmap_lookup_by_phandle_args(struct device_node *np,
> > }
> > EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_phandle_args);
> >
> > +struct regmap *syscon_regmap_lookup_by_phandle_optional(struct device_node *np,
> > + const char *property)
> > +{
> > + struct regmap *regmap;
> > +
> > + regmap = syscon_regmap_lookup_by_phandle(np, property);
> > + if (IS_ERR(regmap) && PTR_ERR(regmap) == -ENODEV)
> > + return NULL;
> > +
> > + return regmap;
> > +}
>
> I think the explanation from the patch description is needed here as well,
> as an interface that might either return an error code or NULL is generally
> a really bad idea. I understand what this is for, but it's easy to misread.
>
> > static inline struct regmap *device_node_to_regmap(struct device_node *np)
> > {
> > @@ -59,6 +62,14 @@ static inline struct regmap *syscon_regmap_lookup_by_phandle_args(
> > {
> > return ERR_PTR(-ENOTSUPP);
> > }
> > +
> > +static inline struct regmap *syscon_regmap_lookup_by_phandle_optional(
> > + struct device_node *np,
> > + const char *property)
> > +{
> > + return ERR_PTR(-ENOTSUPP);
> > +}
>
> Shouldn't this also return NULL then?
>
> Arnd

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