Re: [PATCH 1/1] gpio: core: Decouple open drain/source flag with active low/high

Laxman Dewangan
2017-04-06T17:19:16Z

On Thursday 06 April 2017 09:40 PM, Andy Shevchenko wrote:
> On Thu, Apr 6, 2017 at 4:35 PM, Laxman Dewangan <ldewangan@nvidia.com> wrote:
>> Currently, the GPIO interface is said to Open Drain if it is Single
>> Ended and active LOW. Similarly, it is said as Open Source if it is
>> Single Ended and active HIGH.
>>
>> The active HIGH/LOW is used in the interface for setting the pin
>> state to HIGH or LOW when enabling/disabling the interface.
>>
>> In Open Drain interface, pin is set to HIGH by putting pin in
>> high impedance and LOW by driving to the LOW.
>>
>> In Open Source interface, pin is set to HIGH by driving pin to
>> HIGH and set to LOW by putting pin in high impedance.
>>
>> With above, the Open Drain/Source is unrelated to the active LOW/HIGH
>> in interface. There is interface where the enable/disable of interface
>> is ether active LOW or HIGH but it is Open Drain type.
>>
>> Hence decouple the Open Drain with Single Ended + Active LOW and
>> Open Source with Single Ended + Active HIGH.
>>
>> Adding different flag for the Open Drain/Open Source which is valid
>> only when Single ended flag is enabled.
>> if (single_ended) {
>> - if (active_low)
>> + if (open_drain)
> This breaks ACPI case, right?
>

In acpi case, single_ended is not handled. It only handles the active LOW.

From code:

bool active_low = false;
bool single_ended = false;
int ret;

if (!fwnode)
return ERR_PTR(-EINVAL);

if (is_of_node(fwnode)) {
enum of_gpio_flags flags;

desc = of_get_named_gpiod_flags(to_of_node(fwnode),
propname,
index, &flags);
if (!IS_ERR(desc)) {
active_low = flags & OF_GPIO_ACTIVE_LOW;
single_ended = flags & OF_GPIO_SINGLE_ENDED;
}
} else if (is_acpi_node(fwnode)) {
struct acpi_gpio_info info;

desc = acpi_node_get_gpiod(fwnode, propname, index, &info);
if (!IS_ERR(desc))
active_low = info.polarity == GPIO_ACTIVE_LOW;
}