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[PATCH] gpio: Propagate errors from chip->get()

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  [PATCH] gpio: Propagate errors from chip->get() Bjorn Andersson <bjorn.andersson@sonymobile.com> - 2015-08-29 00:20 +0200
    Re: [PATCH] gpio: Propagate errors from chip->get() Bjorn Andersson <bjorn.andersson@sonymobile.com> - 2015-09-01 07:20 +0200
      Re: [PATCH] gpio: Propagate errors from chip->get() Alexandre Courbot <gnurou@gmail.com> - 2015-09-02 14:40 +0200

#1215589 — [PATCH] gpio: Propagate errors from chip->get()

It's possible to have gpio chips hanging off unreliable remote buses
where the get() operation will fail to acquire a readout of the current
gpio state. Propagate these errors to the consumer so that they can
act on, retry or ignore these failing reads, instead of treating them as
the line being held high.

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
---
 drivers/gpio/gpiolib.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 3b5e516298e0..dc17dbf8c234 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1173,15 +1173,16 @@ EXPORT_SYMBOL_GPL(gpiod_is_active_low);
  * that the GPIO was actually requested.
  */
 
-static bool _gpiod_get_raw_value(const struct gpio_desc *desc)
+static int _gpiod_get_raw_value(const struct gpio_desc *desc)
 {
 	struct gpio_chip	*chip;
-	bool value;
 	int offset;
+	int value;
 
 	chip = desc->chip;
 	offset = gpio_chip_hwgpio(desc);
-	value = chip->get ? chip->get(chip, offset) : false;
+	value = chip->get ? chip->get(chip, offset) : -EIO;
+	value = value < 0 ? value : !!value;
 	trace_gpio_value(desc_to_gpio(desc), 1, value);
 	return value;
 }
@@ -1191,7 +1192,7 @@ static bool _gpiod_get_raw_value(const struct gpio_desc *desc)
  * @desc: gpio whose value will be returned
  *
  * Return the GPIO's raw value, i.e. the value of the physical line disregarding
- * its ACTIVE_LOW status.
+ * its ACTIVE_LOW status, or negative errno on failure.
  *
  * This function should be called from contexts where we cannot sleep, and will
  * complain if the GPIO chip functions potentially sleep.
@@ -1211,7 +1212,7 @@ EXPORT_SYMBOL_GPL(gpiod_get_raw_value);
  * @desc: gpio whose value will be returned
  *
  * Return the GPIO's logical value, i.e. taking the ACTIVE_LOW status into
- * account.
+ * account, or negative errno on failure.
  *
  * This function should be called from contexts where we cannot sleep, and will
  * complain if the GPIO chip functions potentially sleep.
@@ -1225,6 +1226,9 @@ int gpiod_get_value(const struct gpio_desc *desc)
 	WARN_ON(desc->chip->can_sleep);
 
 	value = _gpiod_get_raw_value(desc);
+	if (value < 0)
+		return value;
+
 	if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
 		value = !value;
 
@@ -1547,7 +1551,7 @@ EXPORT_SYMBOL_GPL(gpiochip_unlock_as_irq);
  * @desc: gpio whose value will be returned
  *
  * Return the GPIO's raw value, i.e. the value of the physical line disregarding
- * its ACTIVE_LOW status.
+ * its ACTIVE_LOW status, or negative errno on failure.
  *
  * This function is to be called from contexts that can sleep.
  */
@@ -1565,7 +1569,7 @@ EXPORT_SYMBOL_GPL(gpiod_get_raw_value_cansleep);
  * @desc: gpio whose value will be returned
  *
  * Return the GPIO's logical value, i.e. taking the ACTIVE_LOW status into
- * account.
+ * account, or negative errno on failure.
  *
  * This function is to be called from contexts that can sleep.
  */
@@ -1578,6 +1582,9 @@ int gpiod_get_value_cansleep(const struct gpio_desc *desc)
 		return 0;
 
 	value = _gpiod_get_raw_value(desc);
+	if (value < 0)
+		return value;
+
 	if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
 		value = !value;
 
-- 
1.8.2.2

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#1216595

On Fri 28 Aug 09:44 PDT 2015, Bjorn Andersson wrote:

> It's possible to have gpio chips hanging off unreliable remote buses
> where the get() operation will fail to acquire a readout of the current
> gpio state. Propagate these errors to the consumer so that they can
> act on, retry or ignore these failing reads, instead of treating them as
> the line being held high.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
> ---
>  drivers/gpio/gpiolib.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 3b5e516298e0..dc17dbf8c234 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -1173,15 +1173,16 @@ EXPORT_SYMBOL_GPL(gpiod_is_active_low);
>   * that the GPIO was actually requested.
>   */
>  
> -static bool _gpiod_get_raw_value(const struct gpio_desc *desc)
> +static int _gpiod_get_raw_value(const struct gpio_desc *desc)
>  {
>  	struct gpio_chip	*chip;
> -	bool value;
>  	int offset;
> +	int value;
>  
>  	chip = desc->chip;
>  	offset = gpio_chip_hwgpio(desc);
> -	value = chip->get ? chip->get(chip, offset) : false;
> +	value = chip->get ? chip->get(chip, offset) : -EIO;

Linus, Alexandre, please feel free to apply this with -ENOTSUPP in
accordance to Alexandre's comment in [1], if you prefer that. I picked
-EIO as that's what's used in most other places when the get() op is
missing.

Maybe we should follow up with separate patch to make that consistent?

[1] https://lkml.org/lkml/2015/8/31/8

> +	value = value < 0 ? value : !!value;
>  	trace_gpio_value(desc_to_gpio(desc), 1, value);
>  	return value;
>  }

Regards,
Bjorn
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#1217568

On Tue, Sep 1, 2015 at 2:16 PM, Bjorn Andersson
<bjorn.andersson@sonymobile.com> wrote:
> On Fri 28 Aug 09:44 PDT 2015, Bjorn Andersson wrote:
>
>> It's possible to have gpio chips hanging off unreliable remote buses
>> where the get() operation will fail to acquire a readout of the current
>> gpio state. Propagate these errors to the consumer so that they can
>> act on, retry or ignore these failing reads, instead of treating them as
>> the line being held high.
>>
>> Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
>> ---
>>  drivers/gpio/gpiolib.c | 21 ++++++++++++++-------
>>  1 file changed, 14 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
>> index 3b5e516298e0..dc17dbf8c234 100644
>> --- a/drivers/gpio/gpiolib.c
>> +++ b/drivers/gpio/gpiolib.c
>> @@ -1173,15 +1173,16 @@ EXPORT_SYMBOL_GPL(gpiod_is_active_low);
>>   * that the GPIO was actually requested.
>>   */
>>
>> -static bool _gpiod_get_raw_value(const struct gpio_desc *desc)
>> +static int _gpiod_get_raw_value(const struct gpio_desc *desc)
>>  {
>>       struct gpio_chip        *chip;
>> -     bool value;
>>       int offset;
>> +     int value;
>>
>>       chip = desc->chip;
>>       offset = gpio_chip_hwgpio(desc);
>> -     value = chip->get ? chip->get(chip, offset) : false;
>> +     value = chip->get ? chip->get(chip, offset) : -EIO;
>
> Linus, Alexandre, please feel free to apply this with -ENOTSUPP in
> accordance to Alexandre's comment in [1], if you prefer that. I picked
> -EIO as that's what's used in most other places when the get() op is
> missing.
>
> Maybe we should follow up with separate patch to make that consistent?

I will let Linus decide which value is the more appropriate, the patch
looks solid to me!

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

Thanks!
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