Re: [PATCH v2] gpiolib: return -ENOENT if no GPIO mapping exists

[Alex Courbot <acourbot@nvidia.com>]

On 12/11/2013 12:28 AM, Andy Shevchenko wrote:
> On Tue, 2013-12-10 at 23:37 +0900, Alexandre Courbot wrote:
>> Some devices drivers make use of optional GPIO parameters. For such
>> drivers, it is important to discriminate between the case where no
>> GPIO mapping has been defined for the function they are requesting, and
>> the case where a mapping exists but an error occured while resolving it
>> or when acquiring the GPIO.
>>
>> This patch changes the family of gpiod_get() functions such that they
>> will return -ENOENT if and only if no GPIO mapping is defined for the
>> requested function. Other error codes are used when an actual error
>> occured during the GPIO resolution.
>>
>
> One minor comment below.
> Independently on that:
>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Thanks!

>
>> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
>> ---
>> Changes since v1:
>> - Rebase on top of Linus' devel tree
>> - Fixed error reporting as suggested by Andy
>> ---
>>   Documentation/gpio/consumer.txt |  6 +++++-
>>   drivers/gpio/gpiolib.c          | 33 ++++++++++++++++-----------------
>>   2 files changed, 21 insertions(+), 18 deletions(-)
>>
>> diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
>> index 07c74a3..e42f77d 100644
>> --- a/Documentation/gpio/consumer.txt
>> +++ b/Documentation/gpio/consumer.txt
>> @@ -38,7 +38,11 @@ device that displays digits), an additional index argument can be specified:
>>   					  const char *con_id, unsigned int idx)
>>
>>   Both functions return either a valid GPIO descriptor, or an error code checkable
>> -with IS_ERR(). They will never return a NULL pointer.
>> +with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
>> +if and only if no GPIO has been assigned to the device/function/index triplet,
>> +other error codes are used for cases where a GPIO has been assigned but an error
>> +occured while trying to acquire it. This is useful to discriminate between mere
>> +errors and an absence of GPIO for optional GPIO parameters.
>>
>>   Device-managed variants of these functions are also defined:
>>
>> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
>> index 12e47df..32a6e3a 100644
>> --- a/drivers/gpio/gpiolib.c
>> +++ b/drivers/gpio/gpiolib.c
>> @@ -2367,7 +2367,7 @@ static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
>>   				    unsigned int idx,
>>   				    enum gpio_lookup_flags *flags)
>>   {
>> -	struct gpio_desc *desc = ERR_PTR(-ENODEV);
>> +	struct gpio_desc *desc = ERR_PTR(-ENOENT);
>>   	struct gpiod_lookup_table *table;
>>   	struct gpiod_lookup *p;
>>
>> @@ -2389,19 +2389,21 @@ static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
>>   		chip = find_chip_by_name(p->chip_label);
>>
>>   		if (!chip) {
>> -			dev_warn(dev, "cannot find GPIO chip %s\n",
>> -				 p->chip_label);
>> -			continue;
>> +			dev_err(dev, "cannot find GPIO chip %s\n",
>> +				p->chip_label);
>> +			return ERR_PTR(-ENODEV);
>>   		}
>>
>>   		if (chip->ngpio <= p->chip_hwnum) {
>> -			dev_warn(dev, "GPIO chip %s has %d GPIOs\n",
>> -				 chip->label, chip->ngpio);
>> -			continue;
>> +			dev_err(dev, "requested GPIO %d is out of range [0..%d]"
>> +			       " for chip %s\n", idx, chip->ngpio, chip->label);
>
> You may leave string literals over 80 character border. chackpatch.pl
> will not complain about.
>
> I might put a) 'dev_warn(dev,', b) '"..."', and c) 'the rest'
> on three separate lines.

Oh right, I didn't know you could do that, thanks.

Having the message on a single line is indeed better for grepping. v3 on 
the way...

>
>> +			return ERR_PTR(-EINVAL);
>>   		}
>>
>>   		desc = gpiochip_offset_to_desc(chip, p->chip_hwnum);
>>   		*flags = p->flags;
>> +
>> +		return desc;
>>   	}
>>
>>   	return desc;
>> @@ -2413,7 +2415,8 @@ static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
>>    * @con_id:	function within the GPIO consumer
>>    *
>>    * Return the GPIO descriptor corresponding to the function con_id of device
>> - * dev, or an IS_ERR() condition if an error occured.
>> + * dev, -ENOENT if no GPIO has been assigned to the requested function, or
>> + * another IS_ERR() code if an error occured while trying to acquire the GPIO.
>>    */
>>   struct gpio_desc *__must_check gpiod_get(struct device *dev, const char *con_id)
>>   {
>> @@ -2430,7 +2433,9 @@ EXPORT_SYMBOL_GPL(gpiod_get);
>>    * This variant of gpiod_get() allows to access GPIOs other than the first
>>    * defined one for functions that define several GPIOs.
>>    *
>> - * Return a valid GPIO descriptor, or an IS_ERR() condition in case of error.
>> + * Return a valid GPIO descriptor, -ENOENT if no GPIO has been assigned to the
>> + * requested function and/or index, or another IS_ERR() code if an error
>> + * occured while trying to acquire the GPIO.
>>    */
>>   struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
>>   					       const char *con_id,
>> @@ -2455,15 +2460,9 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
>>   	 * Either we are not using DT or ACPI, or their lookup did not return
>>   	 * a result. In that case, use platform lookup as a fallback.
>>   	 */
>> -	if (!desc || IS_ERR(desc)) {
>> -		struct gpio_desc *pdesc;
>> -
>> +	if (!desc || desc == ERR_PTR(-ENOENT)) {
>>   		dev_dbg(dev, "using lookup tables for GPIO lookup");
>> -		pdesc = gpiod_find(dev, con_id, idx, &flags);
>> -
>> -		/* If used as fallback, do not replace the previous error */
>> -		if (!IS_ERR(pdesc) || !desc)
>> -			desc = pdesc;
>> +		desc = gpiod_find(dev, con_id, idx, &flags);
>>   	}
>>
>>   	if (IS_ERR(desc)) {
>