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

[Martin Peres]

On 06/07/15 16:15, Martin Peres wrote:
> On 06/07/15 16:13, Chris Wilson wrote:
>> 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.
>
> Well, it is not misleading, it just lacks this information.
>
> If it incremented every seconds, the patch would be stupid because the 
> timestamp could be at 0 and polling 10 times at a few us of interval 
> would always yield the same result. That's all :)

Oh, forgot to say: With this information added in the commit message and 
the commit message duplicated as a comment in intel_detect_timestamp(), 
the patch is:

Reviewed-by: Martin Peres <martin.peres at linux.intel.com>