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

[Andrzej Hajda]

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);


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

Regards
Andrzej