Re: [PATCH 1/5] drm/i915: Keep vblank irq enabled during vblank evasion.

Maarten Lankhorst
2018-02-12T15:41:08Z

Op 12-02-18 om 16:31 schreef Chris Wilson:
> Quoting Maarten Lankhorst (2018-02-12 15:27:34)
>> Op 12-02-18 om 16:22 schreef Chris Wilson:
>>> Quoting Maarten Lankhorst (2018-02-12 15:16:39)
>>>> Op 12-02-18 om 16:10 schreef Chris Wilson:
>>>>> Quoting Maarten Lankhorst (2018-02-09 09:54:00)
>>>>>> This is a nice preparation for grabbing the uncore lock during evasion.
>>>>>> Grabbing the spinlock with the lock held messes up the locking,
>>>>>> so it's easier to handover the reference to the eve
>>>>>>
>>>>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>>>>> ---
>>>>>> drivers/gpu/drm/i915/intel_sprite.c | 11 ++++-------
>>>>>> 1 file changed, 4 insertions(+), 7 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
>>>>>> index 3be22c0fcfb5..971a1ea0db45 100644
>>>>>> --- a/drivers/gpu/drm/i915/intel_sprite.c
>>>>>> +++ b/drivers/gpu/drm/i915/intel_sprite.c
>>>>>> @@ -109,10 +109,10 @@ void intel_pipe_update_start(const struct intel_crtc_state *new_crtc_state)
>>>>>>
>>>>>> local_irq_disable();
>>>>>>
>>>>>> - if (min <= 0 || max <= 0)
>>>>>> + if (WARN_ON(drm_crtc_vblank_get(&crtc->base)))
>>>>>> return;
>>>>>>
>>>>>> - if (WARN_ON(drm_crtc_vblank_get(&crtc->base)))
>>>>>> + if (min <= 0 || max <= 0)
>>>>>> return;
>>>>>>
>>>>> The corresponding vblank_put is the one later in update_start(), right?
>>>>> I don't think you intended to keep this chunk.
>>>>> -Chris
>>>> I'm not sure what you mean? The vblank_put is now in pipe_update_end, except if the
>>>> event takes over the reference. I think the code is correct. :)
>>> Then it's unbalanced in the case of error still.
>>> -Chris
>> It already would have been for events, hence the WARN_ON there.
>> I don't think we can do anything about it, this shouldn't ever
>> happen in practice, could be a BUG_ON for all I care. :)
> I would much prefer that over intentionally bad code.
>
> But do we really need to enable the vblank irq here? If the event
> requires it, doesn't it already enable the vblank. Here, we only need it
> when sleeping, can we not determine we have enough time before the
> vblank without enabling the interrupt?
I'm not sure why we get a reference to the vblank counter here. Perhaps Ville does?

~Maarten