[Mesa-dev] [PATCH 01/18] i965: Query whether we have kernel support for the TIMESTAMP register once

Chris Wilson chris at chris-wilson.co.uk
Mon Jul 6 06:13:33 PDT 2015

On Mon, Jul 06, 2015 at 03:10:48PM +0300, Martin Peres wrote:
> On 06/07/15 13:33, Chris Wilson wrote:
> >Move the query for the TIMESTAMP register from context init to the
> >screen, so that it is only queried once for all contexts.
> >
> >On 32bit systems, some old kernels trigger a hw bug resulting in the
> >TIMESTAMP register being shifted and the low bits always zero. Detect
> >this by repeating the read a few times and check the register is
> >incrementing.
> You do not do the latter. You only check for the low bits.
> I guess the counter is supposed to be monotonically increasing and
> with a resolution of a few microseconds which would make this
> perfectly valid. Could you confirm and make sure to add this
> information in the commit message please?

The counter should increment every 80ns. What's misleading in what I
wrote? It describes the hw bug and how to detect it.

Chris Wilson, Intel Open Source Technology Centre

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