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

[Andrzej Hajda]

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.

Btw, tested your warns from another mail, none appeared.

Regards
Andrzej

>
> 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