From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ben Widawsky <ben@bwidawsk.net>
Subject: Re: TIMESTAMP register
Date: Tue, 17 Apr 2012 16:27:45 -0700
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To: Daniel Vetter <daniel@ffwll.ch>
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On Tue, 17 Apr 2012 23:04:18 +0200
Daniel Vetter <daniel@ffwll.ch> wrote:

> On Tue, Apr 17, 2012 at 08:34:11PM +0000, Lawrynowicz, Jacek wrote:
> > ARB_timer_query allows client read TIMESTAMP both asynchronously and synchronously.
> > The former can be implemented as you said but the latter requires support from the KMD.
> > This must be a simple MMIO read as this is the only way to report "current" GPU time.
> > Implementing synchronous TIMESTAMP query using pipe control would render the third example from ARB_timer_query spec useless.
> 
> Ok, I've looked like a dofus again, but now I've read the spec and we
> indeed seem to need a synchronous readout of the TIMESTAMP register. I
> guess a new register will do, together with some fixed-point integer that
> tells userspace how to convert it to nanoseconds.
> -Daniel

I've not read the spec, but synchronous and "current" doesn't mean the
exact same thing to me. I assume the spec doesn't allow getting the
value in a batch and then just waiting for rendering to complete?

If we go with the register read approach, I vote sysfs.