Re: [PATCH v2 14/15] drm/i915/guc: Support OA when Wa_16011777198 is enabled

["Dixit, Ashutosh" <ashutosh.dixit@xxxxxxxxx>]

On Mon, 26 Sep 2022 14:17:21 -0700, Belgaumkar, Vinay wrote:
>
>
> On 9/26/2022 11:19 AM, Umesh Nerlige Ramappa wrote:
> > On Mon, Sep 26, 2022 at 08:56:01AM -0700, Dixit, Ashutosh wrote:
> >> On Fri, 23 Sep 2022 13:11:53 -0700, Umesh Nerlige Ramappa wrote:
> >>>
> >>> From: Vinay Belgaumkar <vinay.belgaumkar@xxxxxxxxx>
> >>
> >> Hi Umesh/Vinay,
> >>
> >>> @@ -3254,6 +3265,24 @@ static int i915_oa_stream_init(struct
> >>> i915_perf_stream *stream,
> >>>     intel_engine_pm_get(stream->engine);
> >>>     intel_uncore_forcewake_get(stream->uncore, FORCEWAKE_ALL);
> >>>
> >>> +    /*
> >>> +     * Wa_16011777198:dg2: GuC resets render as part of the Wa. This
> >>> causes
> >>> +     * OA to lose the configuration state. Prevent this by overriding
> >>> GUCRC
> >>> +     * mode.
> >>> +     */
> >>> +    if (intel_guc_slpc_is_used(&gt->uc.guc) &&
> >>> +        intel_uc_uses_guc_rc(&gt->uc) &&
> >>
> >> Is this condition above correct? E.g. what happens when:
> >>
> >> a. GuCRC is used but SLPC is not used?
>
> Currently, we have no way to separate out GuC RC and SLPC. Both are on when
> guc submission is enabled/supported. So, the above check is kind of
> redundant anyways.

That is why I was suggesting changing the if check to an assert or
drm_err. So looks like it will work with or without GuC RC, but if we are
using GuC RC we should be using SLPC. So:

	if (GuC_RC && !SLPC)
		drm_err();

> Thanks,
>
> Vinay.
>
> >> b. GuCRC is not used. Don't we need to disable RC6 in host based RC6
> >>   control?
> >
> > When using host based rc6, existing OA code is using forcewake and a
> > reference to engine_pm to prevent rc6. Other questions, directing to
> > @Vinay.
> >
> > Thanks,
> > Umesh
> >
> >>
> >> Do we need to worry about these cases?
> >>
> >> Or if we always expect both GuCRC and SLPC to be used on DG2 then I
> >> think
> >> let's get rid of these from the if condition and add a drm_err() if we
> >> see
> >> these not being used and OA is being enabled on DG2?
> >>
> >> Thanks.
> >> --
> >> Ashutosh
> >>
> >>> + (IS_DG2_GRAPHICS_STEP(gt->i915, G10, STEP_A0, STEP_C0) ||
> >>> +         IS_DG2_GRAPHICS_STEP(gt->i915, G11, STEP_A0, STEP_B0))) {
> >>> +        ret = intel_guc_slpc_override_gucrc_mode(&gt->uc.guc.slpc,
> >>> +                             SLPC_GUCRC_MODE_GUCRC_NO_RC6);
> >>> +        if (ret) {
> >>> +            drm_dbg(&stream->perf->i915->drm,
> >>> +                "Unable to override gucrc mode\n");
> >>> +            goto err_config;
> >>> +        }
> >>> +    }
> >>> +
> >>>     ret = alloc_oa_buffer(stream);
> >>>     if (ret)
> >>>         goto err_oa_buf_alloc;
> >>> --
> >>> 2.25.1
> >>>