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

[Ville Syrjälä]

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()).

For normal plane updates the relevant planes are already added
when the property values are updated.

> 
> 
> Let me know if there is better place/way to handle it.
> 
> Regards
> Andrzej

-- 
Ville Syrjälä
Intel