Re: [PATCH 2/2] Documentation: gpio: board: describe the con_id parameter

[Alexandre Courbot <gnurou@xxxxxxxxx>]

On Fri, Aug 21, 2015 at 2:28 AM, Dirk Behme <dirk.behme@xxxxxxxxx> wrote:
> On 25.07.2015 09:11, Dirk Behme wrote:
>>
>> The con_id parameter has to match the GPIO description and is
>> automatically
>> extended by the GPIO suffix if not NULL. I had to look into the code to
>> understand this and properly find the GPIO I've been looking for, so
>> document
>> this.
>>
>> Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxx>
>> ---
>>   Documentation/gpio/board.txt    | 36
>> ++++++++++++++++++++++++++++++++++++
>>   Documentation/gpio/consumer.txt |  3 +++
>>   2 files changed, 39 insertions(+)
>>
>> diff --git a/Documentation/gpio/board.txt b/Documentation/gpio/board.txt
>> index 7605773..eac78fc 100644
>> --- a/Documentation/gpio/board.txt
>> +++ b/Documentation/gpio/board.txt
>> @@ -48,6 +48,42 @@ This property will make GPIOs 15, 16 and 17 available
>> to the driver under the
>>   The led GPIOs will be active-high, while the power GPIO will be
>> active-low (i.e.
>>   gpiod_is_active_low(power) will be true).
>>
>> +If in the consumer device's node the property doesn't have a <function>-
>> prefix,
>> +the second parameter (con_id) of the gpiod_get*() functions has to be
>> NULL:
>> +
>> +E.g. if in the above device tree example the GPIO array is just called
>> 'gpios'
>> +
>> +       foo_device {
>> +               compatible = "acme,foo";
>> +               ...
>> +               gpios = <&gpio 15 GPIO_ACTIVE_HIGH>, /* red */
>> +                       <&gpio 16 GPIO_ACTIVE_HIGH>, /* green */
>> +                       <&gpio 17 GPIO_ACTIVE_HIGH>; /* blue */
>> +       };
>> +
>> +the gpiod_get*() calls will be:
>> +
>> +       struct gpio_desc *red, *green, *blue, *power;
>> +
>> +       red = gpiod_get_index(dev, NULL, 0, GPIOD_OUT_HIGH);
>> +       green = gpiod_get_index(dev, NULL, 1, GPIOD_OUT_HIGH);
>> +       blue = gpiod_get_index(dev, NULL, 2, GPIOD_OUT_HIGH);
>> +
>> +To summarize:
>> +
>> +The con_id string parameter has to be either NULL or the
>> <function>-prefix
>> +of the GPIO suffixes ("gpios" or "gpio", automatically looked up by the
>> +gpiod functions internally):
>> +
>> +* If the GPIO description is just named with one of the GPIO suffixes
>> +  ("gpios" or "gpio"), use NULL.
>> +* If the GPIO description is prefixed with anything, e.g. "led-gpios",
>> use the
>> +  prefix without the "-" as con_id parameter (in this example "led").
>> +
>> +In case con_id is not NULL, the GPIO subsystem prefixes the GPIO suffix
>> +("gpios" or "gpio") with the string passed in con_id to get the resulting
>> string
>> +(snprintf(... "%s-%s", con_id, gpio_suffixes[]).
>> +
>>   ACPI
>>   ----
>>   ACPI also supports function names for GPIOs in a similar fashion to DT.
>> diff --git a/Documentation/gpio/consumer.txt
>> b/Documentation/gpio/consumer.txt
>> index 75542b9..47ce4fd 100644
>> --- a/Documentation/gpio/consumer.txt
>> +++ b/Documentation/gpio/consumer.txt
>> @@ -39,6 +39,9 @@ device that displays digits), an additional index
>> argument can be specified:
>>                                           const char *con_id, unsigned int
>> idx,
>>                                           enum gpiod_flags flags)
>>
>> +For a more detailed description of the con_id parameter in the DeviceTree
>> case
>> +see Documentation/gpio/board.txt
>> +
>>   The flags parameter is used to optionally specify a direction and
>> initial value
>>   for the GPIO. Values can be:
>
>
>
> Any further comments on this? Or could this be applied?

Using the "gpios" property is considered deprecated, so I am not sure
that is a good idea to mention this too extensively in the boards file
(people might be tempted to use that option while we clearly don't
want them to).

A precise description of the lookup method is clearly missing though.
I don't know what the right place would be for it. consumer.txt?
board.txt in a more concise (and with a big "DEPRECATED") way?
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