[PATCH RESEND v2 1/2] dma-fence: allow signaling drivers to set fence timestamp

[John Stultz]

On Thu, Jan 7, 2021 at 12:53 AM Veera Sundaram Sankaran
<veeras at codeaurora.org> wrote:
>
> Some drivers have hardware capability to get the precise timestamp of
> certain events based on which the fences are triggered. This allows it to
> set accurate timestamp factoring out any software and IRQ latencies. Add
> a timestamp variant of fence signal function, dma_fence_signal_timestamp
> to allow drivers to update the precise timestamp for fences.
>

So, on quick review, this seems mostly sane. Though, it might be good
to add some more detail about how the hardware timestamping fits into
the kernel's CLOCK_MONOTONIC time domain.

I just want to make sure this interface isn't abused to jam raw
hardware-domain timestamps into the fence->timestamp, causing the
meaning or time-domain of the fence->timestamp to be unclear or
inconsistent.

It may be useful to add an additional patch to the documentation
around the dma_fence structure to make the timestamp field semantics
more explicit and avoid confusion?

thanks
-john