Re: Query about Open drain flag with active LOW

[Laxman Dewangan <ldewangan@nvidia.com>]

On Tuesday 28 March 2017 02:36 PM, Linus Walleij wrote:
> On Mon, Mar 27, 2017 at 5:21 PM, Laxman Dewangan <ldewangan@nvidia.com> wrote:
>
>> I have the schematics, where I need to set it as
>> Pin state HIGH (by setting gpio-input mode) to enable the circuit.
>> Pin state LOW (by setting gpio-output mode with value to 0) to disable the
>> circuit.
> (...)
>> With this, I think the GPIO is active HIGH and open drain type.
>> If I set the active LOW from DT then I can not set pin to logical 1 using
>> the API gpiod_set_value() with “1”.
>> As this invert before calling _gpiod_set_raw_value() and so the value = 0
>> and it set the pin in the gpio mode output-Low.
>>
>> Shouldn'’t open drain pin are active HIGH?
> Sorry I do not understand, have you solved it?

I wanted to say that open drain flag should be with ACTIVE_HIGH | 
SINGLE_ENDED which is in inverted as of now.



> Else can you try to break down the problem, do you mean there is a bug
> in inverted handling for open drain lines in gpiolib?
>

Yes, I am suspecting the bug here with combination of ACTIVE state and 
SINGLE_ENDED flag. The logic to get OPEN DRAIN flag should be in 
inverted form.
Else we need to decouple the ACTIVE state with SINGLE_ENDED flag to get 
Open drain or open source.


If I want to say logical "1" for the open drain, it is setting pin in 
drive-0 mode. Actually, it should be in input mode so that pin state 
become HIGH.

In function of_find_gpio(), it is as follows:

         if (of_flags & OF_GPIO_SINGLE_ENDED) {
                 if (of_flags & OF_GPIO_ACTIVE_LOW)
                         *flags |= GPIO_OPEN_DRAIN;
                 else
                         *flags |= GPIO_OPEN_SOURCE;
         }


I think it should be
         if (of_flags & OF_GPIO_SINGLE_ENDED) {
                 if (of_flags & OF_GPIO_ACTIVE_LOW)
                         *flags |= GPIO_OPEN_SOURCE;
                 else
                         *flags |= GPIO_OPEN_DRAIN;
         }


Similar change is needed in the dtbinding gpio header also to invert the 
ACTIVE state with open drain/source.


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