[PATCH 1/3] drm/panfrost: Add SYSTEM_TIMESTAMP and SYSTEM_TIMESTAMP_FREQUENCY parameters

[Mary Guillemard]

Hello Steve,

> VK_KHR_calibrated_timestamps says it should query 'quasi simultaneously
> from two time domains' - but this is purely providing an interface to
> read a single counter at a time.
> 
> It _may_ be useful to report the GPU's view of time and at the same time
> (or as near as possible) the architectural counters. That can be used to
> deal with drift between the GPU's counters and arch counters[1].
> 
> In general we try to avoid providing an interface to something which is
> unrelated to the GPU, especially when user space already has a mechanism.
> 
> Steve
> 
> [1] See Mihail's response to the panthor patches for details of
> differences that might occur.

I initially didn't saw the register to get the GPU timestamp and
wrongly assumed I would have to query it from the generic arch timer.

I will make SYSTEM_TIMESTAMP returns the value of the timestamp register
on v2 and keep SYSTEM_TIMESTAMP_FREQUENCY the same way as it is at the
moment.

Thanks for the review,

Mary