Re: [RFC] libgpiod public API reviews needed

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Sun, Jan 21, 2018 at 11:18 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Sun, Jan 21, 2018 at 10:30 PM, Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
>> 2018-01-21 16:49 GMT+01:00 Linus Walleij <linus.walleij@xxxxxxxxxx>:
>>> On Fri, Jan 19, 2018 at 2:28 PM, Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
>
>> I was not aware of this, but it seems you're right! Nice catch, thanks.
>>
>> How about defining a local struct gpiod_timespec with both seconds and
>> nanoseconds explicitly defined to uint64_t?
>
> Where is that timestamp generated? Is this purely a user space interface
> with the time read from gettimeofday(), or are we talking about  a new
> kernel-to-user interface?

This is in include/uapi/linux/gpio.h:

/**
 * struct gpioevent_data - The actual event being pushed to userspace
 * @timestamp: best estimate of time of event occurrence, in nanoseconds
 * @id: event identifier
 */
struct gpioevent_data {
        __u64 timestamp;
        __u32 id;
};

It is the same as is used for IIO. Inside the kernel this ultimately
comes from ktime_get_real_ns();

> In a lot of cases, a simple 64-bit nanosecond counter using CLOCK_MONOTONIC
> timestamps is the most robust and simple solution.

Bartosz also seems to think it is the best so would vote to go
for that and we have one problem less.

Yours,
Linus Walleij
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