Re: [Intel-gfx] [PATCH] drm/i915: do not reset PLANE_SURF on plane disable on older gens

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Sep 06, 2022 at 03:57:37PM +0200, Andrzej Hajda wrote:
> 
> 
> On 06.09.2022 13:22, Ville Syrjälä wrote:
> > On Tue, Sep 06, 2022 at 01:09:16PM +0200, Andrzej Hajda wrote:
> >>
> >> On 05.09.2022 19:44, Ville Syrjälä wrote:
> >>> On Mon, Sep 05, 2022 at 07:02:40PM +0200, Andrzej Hajda wrote:
> >>>> On 05.09.2022 13:48, Ville Syrjälä wrote:
> >>>>> On Mon, Sep 05, 2022 at 10:05:00AM +0200, Andrzej Hajda wrote:
> >>>>>> In case of ICL and older generations disabling plane and/or disabling
> >>>>>> async update is always performed on vblank,
> >>>>> It should only be broken on bdw-glk (see. need_async_flip_disable_wa).
> >>>> On CFL it is reported every drmtip run:
> >>>> https://intel-gfx-ci.01.org/tree/drm-tip/drmtip.html?testfilter=tiled-max-hw
> >>>> https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_1209/fi-cfl-8109u/igt@kms_big_fb@yf-tiled-max-hw-stride-32bpp-rotate-180-async-flip.html#dmesg-warnings402
> >>>> https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_1209/fi-cfl-8109u/igt@kms_big_fb@y-tiled-max-hw-stride-64bpp-rotate-180-async-flip.html#dmesg-warnings402
> >>>> https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_1209/fi-cfl-8109u/igt@kms_big_fb@y-tiled-max-hw-stride-32bpp-rotate-180-async-flip.html
> >>>> https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_1208/fi-cfl-8109u/igt@kms_big_fb@y-tiled-max-hw-stride-64bpp-rotate-180-async-flip.html
> >>>> ...
> >>>> On APL it is less frequent, probably due to other bugs preventing run of
> >>>> this test, last seen at:
> >>>> https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_1190/fi-apl-guc/igt@kms_big_fb@y-tiled-max-hw-stride-32bpp-rotate-180-async-flip.html
> >>>> Similar for SKL:
> >>>> https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_1181/fi-skl-guc/igt@kms_big_fb@x-tiled-max-hw-stride-64bpp-rotate-180-async-flip.html
> >>>>
> >>>> I am not sure if I correctly read the docs but [1] says that 9th bit of
> >>>> PLANE_CFG (Async Address Update Enable) is "not double buffered and the
> >>>> changes will apply immediately" only for ICL, JSL, LKF1.
> >>> It got broken in bdw and fixed again in icl.
> >>>
> >>>> So the change is not necessary in case of icl_plane_disable_arm.
> >>>>
> >>>> [1]: https://gfxspecs.intel.com/Predator/Home/Index/7656
> >>>>>> but if async update is enabled
> >>>>>> PLANE_SURF register is updated asynchronously. Writing 0 to PLANE_SURF
> >>>>>> when plane is still enabled can cause DMAR/PIPE errors.
> >>>>>> On the other side PLANE_SURF is used to arm plane registers - we need to
> >>>>>> write to it to trigger update on VBLANK, writting current value should
> >>>>>> be safe - the buffer address is valid till vblank.
> >>>>> I think you're effectively saying that somehow the async
> >>>>> flip disable w/a is not kicking in sometimes.
> >>>> I was not aware of existence of this w/a and I am little lost in
> >>>> figuring out how this w/a can prevent zeroing PLANE_SURF too early.
> >>> When it works as designed it should:
> >>> 1. turn off the async flip bit
> >>> 2. wait for vblank so that gets latched
> >>> 3. do the sync plane update/disable normally
> >> After debugging this terra incognita, I've figured out that plane states
> >> are not populated in intel_crtc_async_flip_disable_wa
> >> so for_each_old_intel_plane_in_state does not iterate over affected
> >> planes and w/a does not work at all.
> >> I have no idea where affected plane states should be added.
> >> Adding them to the beginning of intel_atomic_check helped, but this is
> >> just blind shot:
> >>
> >> @@ -6778,10 +6778,14 @@ static int intel_atomic_check(struct drm_device
> >> *dev,
> >>                new_crtc_state->uapi.mode_changed = true;
> >>
> >>            if (new_crtc_state->uapi.scaling_filter !=
> >>                old_crtc_state->uapi.scaling_filter)
> >>                new_crtc_state->uapi.mode_changed = true;
> >> +
> >> +        ret = intel_atomic_add_affected_planes(state, crtc);
> >> +        if (ret)
> >> +            goto fail;
> >>        }
> >>
> >>        intel_vrr_check_modeset(state);
> >>
> >>        ret = drm_atomic_helper_check_modeset(dev, &state->base);
> >                ^
> > This guy should be adding them for any crtc that has been flagged
> > for modeset ahead of time. For modesets flagged later we have to
> > add them by hand (eg. in intel_modeset_all_pipes()).
> 
> This is no-modeset scenario, drm_atomic_helper_check_modeset does not 
> add planes in this case.

Then he mystery is how intel_crtc_async_flip_disable_wa() manages
to not disable async flip for some planes...

-- 
Ville Syrjälä
Intel