Re: [PATCH 04/10] drm/i915: add RPS configuration for Haswell

[Ben Widawsky <ben@bwidawsk.net>]

On Mon, 02 Jul 2012 17:02:59 -0300
Eugeni Dodonov <eugeni.dodonov@linux.intel.com> wrote:

> On 07/02/2012 02:49 PM, Ben Widawsky wrote:
> > On Mon,  2 Jul 2012 11:51:05 -0300
> > Eugeni Dodonov <eugeni.dodonov@intel.com> wrote:
> > 
> >> Most of the RPS and RC6 enabling functionality is similar to what we had
> >> on Gen6/Gen7, so we preserve most of the registers.
> >>
> >> Note that Haswell only has RC6, so account for that as well. As suggested
> >> by Daniel Vetter, to reduce the amount of changes in the patch, we still
> >> write the RC6p/RC6pp thresholds, but those are ignored on Haswell.
> >>
> >> Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
> > Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
> 
> Daniel, to please Ben Widawsky, you could add an extra paragraph in my
> message, saying:
> 
> 'On Haswell, the suggested values for the RP UP and RP DOWN interrupts
> have changed in a way to have lower thresholds for all the operations.
> However, the suggested values for pre-Haswell machines stay the same. In
> order to follow what the hardware designers suggest, we program those as
> suggested for each generation now.
> 
> Also, Haswell introduces a new scheduling bit for the RP DOWN
> scheduling, which we now use by default'.
> 
> Eugeni

The code itself states the above perfectly well. I was really trying
to understand the, "why."


-- 
Ben Widawsky, Intel Open Source Technology Center