Re: [PATCH v2] Documentation: gpio: consumer: describe active low property

[Alexandre Courbot <acourbot@nvidia.com>]

On 08/15/2015 02:46 PM, Dirk Behme wrote:
> On 18.07.2015 08:02, Dirk Behme wrote:
>> I've been searching for any documentation of 'the active-low property
>> of a GPIO'
>> already mentioned in this documenation. But couldn't find any. Add it.
>>
>> Sigend-off-by: Dirk Behme <dirk.behme@gmail.com>
>> Acked-by: Alexandre Courbot <acourbot@nvidia.com>
>> ---
>> Changes in v2: Incorporate the review comments from Alexandre.
>>
>>   Documentation/gpio/consumer.txt | 33 +++++++++++++++++++++++++++++++++
>>   1 file changed, 33 insertions(+)
>>
>> diff --git a/Documentation/gpio/consumer.txt
>> b/Documentation/gpio/consumer.txt
>> index 75542b9..df7c51a 100644
>> --- a/Documentation/gpio/consumer.txt
>> +++ b/Documentation/gpio/consumer.txt
>> @@ -237,6 +237,39 @@ Note that these functions should only be used
>> with great moderation ; a driver
>>   should not have to care about the physical line level.
>>
>>
>> +The active-low property
>> +-----------------------
>> +
>> +As a driver should not have to care about the physical line level,
>> all of the
>> +gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions
>> operate with
>> +the *logical* value. With this they take the active-low property into
>> account.
>> +This does mean that they check whether the GPIO is configured to be
>> active-low.
>> +And if so, they manipulate the passed value before the physical line
>> level is
>> +driven.
>> +
>> +With this, all the gpiod_set_(array)_value_xxx() functions interpret
>> the parameter
>> +"value" as "active" ("1") or "inactive" ("0"). The physical line
>> level will be
>> +driven accordingly.
>> +
>> +As an example, if the active-low poperty for a dedicated GPIO is set,
>> and the
>> +gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical
>> line level will be
>> +driven low.
>> +
>> +To summarize:
>> +
>> +Function (example)               active-low proporty  physical line
>> +gpiod_set_raw_value(desc, 0);        don't care           low
>> +gpiod_set_raw_value(desc, 1);        don't care           high
>> +gpiod_set_value(desc, 0);       default (active-high)     low
>> +gpiod_set_value(desc, 1);       default (active-high)     high
>> +gpiod_set_value(desc, 0);             active-low          high
>> +gpiod_set_value(desc, 1);             active-low          low
>> +
>> +Please note again that the set_raw/get_raw functions should be
>> avoided as much
>> +as possible, especially by drivers which should not care about the
>> actual physical
>> +line level and worry about the logical value instead.
>> +
>> +
>>   Set multiple GPIO outputs with a single function call
>>   -----------------------------------------------------
>>   The following functions set the output values of an array of GPIOs:
>
>
> Any further comments on this? Could this be applied?

I am ok with it - Linus?