gpio: return NULL from gpiod_get_optional when GPIOLIB is disabled
diff mbox

Message ID 20150220003035.GA22334@dtor-glaptop
State New
Headers show

Commit Message

Dmitry Torokhov Feb. 20, 2015, 12:30 a.m. UTC
Given the intent behind gpiod_get_optional() and friends it does not make
sense to return -ENOSYS when GPIOLIB is disabled: the driver is expected to
work just fine without gpio so let's behave as if gpio was not found.
Otherwise we have to special-case -ENOSYS in drivers.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 include/linux/gpio/consumer.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Alexandre Courbot Feb. 20, 2015, 4:59 a.m. UTC | #1
On Fri, Feb 20, 2015 at 9:30 AM, Dmitry Torokhov
<dmitry.torokhov@gmail.com> wrote:
> Given the intent behind gpiod_get_optional() and friends it does not make
> sense to return -ENOSYS when GPIOLIB is disabled: the driver is expected to
> work just fine without gpio so let's behave as if gpio was not found.
> Otherwise we have to special-case -ENOSYS in drivers.

Interestingly Uwe sent a RFC for this one week ago:

http://patchwork.ozlabs.org/patch/439135/

Maybe credit him with a Suggested-by.?

I should have commented at that time, but let's do it now: I agree
with the idea, but this leaves the door open to confusing situations
in case gpiolib was unintentionally disabled. Could you also add a
note in the documentation of this function to explain this behavior,
to spare a few headaches to users of this function?

>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> ---
>  include/linux/gpio/consumer.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> index fd85cb1..f68244f 100644
> --- a/include/linux/gpio/consumer.h
> +++ b/include/linux/gpio/consumer.h
> @@ -132,14 +132,14 @@ static inline struct gpio_desc *__must_check
>  __gpiod_get_optional(struct device *dev, const char *con_id,
>                      enum gpiod_flags flags)
>  {
> -       return ERR_PTR(-ENOSYS);
> +       return NULL;
>  }
>
>  static inline struct gpio_desc *__must_check
>  __gpiod_get_index_optional(struct device *dev, const char *con_id,
>                            unsigned int index, enum gpiod_flags flags)
>  {
> -       return ERR_PTR(-ENOSYS);
> +       return NULL;
>  }
>
>  static inline void gpiod_put(struct gpio_desc *desc)
> @@ -171,14 +171,14 @@ static inline struct gpio_desc *__must_check
>  __devm_gpiod_get_optional(struct device *dev, const char *con_id,
>                           enum gpiod_flags flags)
>  {
> -       return ERR_PTR(-ENOSYS);
> +       return NULL;
>  }
>
>  static inline struct gpio_desc *__must_check
>  __devm_gpiod_get_index_optional(struct device *dev, const char *con_id,
>                                 unsigned int index, enum gpiod_flags flags)
>  {
> -       return ERR_PTR(-ENOSYS);
> +       return NULL;
>  }
>
>  static inline void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
> --
> 2.2.0.rc0.207.ga3a616c
>
>
> --
> Dmitry
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Dmitry Torokhov Feb. 20, 2015, 5:33 a.m. UTC | #2
On Fri, Feb 20, 2015 at 01:59:43PM +0900, Alexandre Courbot wrote:
> On Fri, Feb 20, 2015 at 9:30 AM, Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> > Given the intent behind gpiod_get_optional() and friends it does not make
> > sense to return -ENOSYS when GPIOLIB is disabled: the driver is expected to
> > work just fine without gpio so let's behave as if gpio was not found.
> > Otherwise we have to special-case -ENOSYS in drivers.
> 
> Interestingly Uwe sent a RFC for this one week ago:
> 
> http://patchwork.ozlabs.org/patch/439135/
> 
> Maybe credit him with a Suggested-by.?

I certainly am fine with crediting him with Suggested-by even though I did not
see that Uwe's e-mail but this patch was prompted by his other patch changing a
few input drivers to use gpiod_get_optional() and me recalling that I
explicitly did not use it as it made no difference from gpiod_get() since I had
to handle -ENOSYS anyway.

> 
> I should have commented at that time, but let's do it now: I agree
> with the idea, but this leaves the door open to confusing situations
> in case gpiolib was unintentionally disabled. Could you also add a
> note in the documentation of this function to explain this behavior,
> to spare a few headaches to users of this function?

You mean the inline documentation in drivers/gpio/gpiolib.c and
drivers/gpio/devres.c? I can certainly mention there that is GPIOLIB is disabled
thy will return NULL unlike the non-optional variants.

> 
> >
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> > ---
> >  include/linux/gpio/consumer.h | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> > index fd85cb1..f68244f 100644
> > --- a/include/linux/gpio/consumer.h
> > +++ b/include/linux/gpio/consumer.h
> > @@ -132,14 +132,14 @@ static inline struct gpio_desc *__must_check
> >  __gpiod_get_optional(struct device *dev, const char *con_id,
> >                      enum gpiod_flags flags)
> >  {
> > -       return ERR_PTR(-ENOSYS);
> > +       return NULL;
> >  }
> >
> >  static inline struct gpio_desc *__must_check
> >  __gpiod_get_index_optional(struct device *dev, const char *con_id,
> >                            unsigned int index, enum gpiod_flags flags)
> >  {
> > -       return ERR_PTR(-ENOSYS);
> > +       return NULL;
> >  }
> >
> >  static inline void gpiod_put(struct gpio_desc *desc)
> > @@ -171,14 +171,14 @@ static inline struct gpio_desc *__must_check
> >  __devm_gpiod_get_optional(struct device *dev, const char *con_id,
> >                           enum gpiod_flags flags)
> >  {
> > -       return ERR_PTR(-ENOSYS);
> > +       return NULL;
> >  }
> >
> >  static inline struct gpio_desc *__must_check
> >  __devm_gpiod_get_index_optional(struct device *dev, const char *con_id,
> >                                 unsigned int index, enum gpiod_flags flags)
> >  {
> > -       return ERR_PTR(-ENOSYS);
> > +       return NULL;
> >  }
> >
> >  static inline void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
> > --
> > 2.2.0.rc0.207.ga3a616c
> >
> >
> > --
> > Dmitry
Alexandre Courbot Feb. 20, 2015, 5:37 a.m. UTC | #3
On Fri, Feb 20, 2015 at 2:33 PM, Dmitry Torokhov
<dmitry.torokhov@gmail.com> wrote:
>> I should have commented at that time, but let's do it now: I agree
>> with the idea, but this leaves the door open to confusing situations
>> in case gpiolib was unintentionally disabled. Could you also add a
>> note in the documentation of this function to explain this behavior,
>> to spare a few headaches to users of this function?
>
> You mean the inline documentation in drivers/gpio/gpiolib.c and
> drivers/gpio/devres.c? I can certainly mention there that is GPIOLIB is disabled
> thy will return NULL unlike the non-optional variants.

I was thinking about Documentation/gpio/consumer.txt, but having a
note in the inline documentation as well certainly makes sense.
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Uwe Kleine-K├Ânig Feb. 20, 2015, 6:54 p.m. UTC | #4
Hello,

On Thu, Feb 19, 2015 at 09:33:44PM -0800, Dmitry Torokhov wrote:
> On Fri, Feb 20, 2015 at 01:59:43PM +0900, Alexandre Courbot wrote:
> > On Fri, Feb 20, 2015 at 9:30 AM, Dmitry Torokhov
> > <dmitry.torokhov@gmail.com> wrote:
> > > Given the intent behind gpiod_get_optional() and friends it does not make
> > > sense to return -ENOSYS when GPIOLIB is disabled: the driver is expected to
> > > work just fine without gpio so let's behave as if gpio was not found.
> > > Otherwise we have to special-case -ENOSYS in drivers.
> > 
> > Interestingly Uwe sent a RFC for this one week ago:
> > 
> > http://patchwork.ozlabs.org/patch/439135/
> > 
> > Maybe credit him with a Suggested-by.?
> 
> I certainly am fine with crediting him with Suggested-by even though I did not
> see that Uwe's e-mail but this patch was prompted by his other patch changing a
> few input drivers to use gpiod_get_optional() and me recalling that I
> explicitly did not use it as it made no difference from gpiod_get() since I had
> to handle -ENOSYS anyway.
Note that I'm not convinced any more this is a good idea. Consider you
have a device tree entry specifying 

	reset-gpio = <&gpio5 4 0>;

for your device.

With

	gpiod_get_optional(dev, "reset", GPIO_OUT_LOW);

the drivers tells that some of the devices it can handle have a reset
gpio. If the device in question does have such a gpio the driver must
know and do something with it. If the device doesn't have such a gpio
that's fine, too.

But if GPIOLIB is off and the device has a reset-gpio specified you
certainly want to error out, right?

So IMHO the right thing to do is to return NULL iff there is no
reset-gpio specified. Otherwise -ENOSYS is the right thing to return.

Best regards
Uwe

Patch
diff mbox

diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index fd85cb1..f68244f 100644
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -132,14 +132,14 @@  static inline struct gpio_desc *__must_check
 __gpiod_get_optional(struct device *dev, const char *con_id,
 		     enum gpiod_flags flags)
 {
-	return ERR_PTR(-ENOSYS);
+	return NULL;
 }
 
 static inline struct gpio_desc *__must_check
 __gpiod_get_index_optional(struct device *dev, const char *con_id,
 			   unsigned int index, enum gpiod_flags flags)
 {
-	return ERR_PTR(-ENOSYS);
+	return NULL;
 }
 
 static inline void gpiod_put(struct gpio_desc *desc)
@@ -171,14 +171,14 @@  static inline struct gpio_desc *__must_check
 __devm_gpiod_get_optional(struct device *dev, const char *con_id,
 			  enum gpiod_flags flags)
 {
-	return ERR_PTR(-ENOSYS);
+	return NULL;
 }
 
 static inline struct gpio_desc *__must_check
 __devm_gpiod_get_index_optional(struct device *dev, const char *con_id,
 				unsigned int index, enum gpiod_flags flags)
 {
-	return ERR_PTR(-ENOSYS);
+	return NULL;
 }
 
 static inline void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)