[PATCH] mfd: syscon: Add syscon_regmap_lookup_by_phandle_optional() function.

[PATCH] mfd: syscon: Add syscon_regmap_lookup_by_phandle_optional() function.

[Enric Balletbo i Serra]

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>
---

 drivers/mfd/syscon.c       | 13 +++++++++++++
 include/linux/mfd/syscon.h | 11 +++++++++++
 2 files changed, 24 insertions(+)

diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
index ca465794ea9c..60c5c2b194cc 100644
--- a/drivers/mfd/syscon.c
+++ b/drivers/mfd/syscon.c
@@ -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;
+}
+EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_phandle_optional);
+
 static int syscon_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
diff --git a/include/linux/mfd/syscon.h b/include/linux/mfd/syscon.h
index 7f20e9b502a5..a1fe8aedced2 100644
--- a/include/linux/mfd/syscon.h
+++ b/include/linux/mfd/syscon.h
@@ -28,6 +28,9 @@ extern struct regmap *syscon_regmap_lookup_by_phandle_args(
 					const char *property,
 					int arg_count,
 					unsigned int *out_args);
+extern struct regmap *syscon_regmap_lookup_by_phandle_optional(
+					struct device_node *np,
+					const char *property);
 #else
 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);
+}
+
 #endif
 
 #endif /* __LINUX_MFD_SYSCON_H__ */
-- 
2.28.0

Re: [PATCH] mfd: syscon: Add syscon_regmap_lookup_by_phandle_optional() function.

[Matthias Brugger]

On 27/10/2020 22:11, Enric Balletbo i Serra 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>

Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>

> ---
> 
>   drivers/mfd/syscon.c       | 13 +++++++++++++
>   include/linux/mfd/syscon.h | 11 +++++++++++
>   2 files changed, 24 insertions(+)
> 
> diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
> index ca465794ea9c..60c5c2b194cc 100644
> --- a/drivers/mfd/syscon.c
> +++ b/drivers/mfd/syscon.c
> @@ -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;
> +}
> +EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_phandle_optional);
> +
>   static int syscon_probe(struct platform_device *pdev)
>   {
>   	struct device *dev = &pdev->dev;
> diff --git a/include/linux/mfd/syscon.h b/include/linux/mfd/syscon.h
> index 7f20e9b502a5..a1fe8aedced2 100644
> --- a/include/linux/mfd/syscon.h
> +++ b/include/linux/mfd/syscon.h
> @@ -28,6 +28,9 @@ extern struct regmap *syscon_regmap_lookup_by_phandle_args(
>   					const char *property,
>   					int arg_count,
>   					unsigned int *out_args);
> +extern struct regmap *syscon_regmap_lookup_by_phandle_optional(
> +					struct device_node *np,
> +					const char *property);
>   #else
>   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);
> +}
> +
>   #endif
>   
>   #endif /* __LINUX_MFD_SYSCON_H__ */
> 

Re: [PATCH] mfd: syscon: Add syscon_regmap_lookup_by_phandle_optional() function.

[Arnd Bergmann]

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