# Re: \[RFC 08/11\] gpiolib: cdev: Add hardware timestamp clock type

- From: Dipen Patel \<dipenp@nvidia.com\>
- Date: 2021-07-30 03:07:09 
- List: linux-gpio
- Page: https://ratatoskr.run/linux-gpio/2021/07/1462767
- Thread: https://ratatoskr.run/linux-tegra/2021/06/1426429/t.md

```text

On 6/27/21 4:49 AM, Linus Walleij wrote:
> On Sat, Jun 26, 2021 at 1:48 AM Dipen Patel [ref] wrote:
>
> Just a quick question about this:
>
>> +        GPIO_V2_LINE_FLAG_EVENT_CLOCK_HARDWARE | \
> Is the usage intended to be such that since hardware timestamp
> can not be guaranteed we need to ask for it and fail and if that
> fails maybe the software wants to fall back to the realtime or
> common timestamp?
>
> I'm thinking from the view of libgpiod or similar apps that abstract
> this and they will be "I want to use hardware timestamps if and
> only if it is available, otherwise I want to use this other timestamp"
> or is that use case uncommon, such that either you know exactly
> what you want or you should not be messing with hardware
> timestamps?


The way currently is implemented, if you have requested

FLAG_EVENT_CLOCK_HARDWARE and it fails, control will return

to userspace with an error. There is no fallback.

>
> Yours,
> Linus Walleij
```