Re: [PATCH] drm/i915: Assert we hold the CRTC powerwell for generating vblank interrupts

Maarten Lankhorst
2016-10-11T07:45:47Z

Op 11-10-16 om 08:55 schreef Ville Syrjälä:
> On Tue, Oct 11, 2016 at 08:17:22AM +0200, Maarten Lankhorst wrote:
>> Op 10-10-16 om 13:56 schreef Ville Syrjälä:
>>> On Mon, Oct 10, 2016 at 12:46:32PM +0100, Chris Wilson wrote:
>>>> On Mon, Oct 10, 2016 at 02:42:01PM +0300, Ville Syrjälä wrote:
>>>>> On Mon, Oct 10, 2016 at 12:34:54PM +0100, Chris Wilson wrote:
>>>>>> To enable the vblank itself, we need to have an RPM wakeref for the mmio
>>>>>> access, and whilst generating the vblank interrupts we continue to
>>>>>> require the rpm wakeref. The assumption is that the RPM wakeref is held
>>>>>> by the display powerwell held by the active pipe. As this chain was not
>>>>>> obvious to me chasing the drm_wait_vblank ioctl, document it with a WARN
>>>>>> during *_vblank_enable().
>>>>>>
>>>>>> v2: Check the display power well rather than digging inside the atomic
>>>>>> CRTC state.
>>>>>>
>>>>>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>>>>>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>>>>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>>>>> ---
>>>>>> drivers/gpu/drm/i915/i915_irq.c | 20 ++++++++++++++++++++
>>>>>> 1 file changed, 20 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
>>>>>> index 1e43fe30da11..f0f17055dbb9 100644
>>>>>> --- a/drivers/gpu/drm/i915/i915_irq.c
>>>>>> +++ b/drivers/gpu/drm/i915/i915_irq.c
>>>>>> @@ -2715,6 +2715,14 @@ void i915_handle_error(struct drm_i915_private *dev_priv,
>>>>>> i915_reset_and_wakeup(dev_priv);
>>>>>> }
>>>>>>
>>>>>> +static void assert_pipe_is_awake(struct drm_i915_private *dev_priv,
>>>>>> + enum pipe pipe)
>>>>>> +{
>>>>>> + WARN_ON(IS_ENABLED(CONFIG_DRM_I915_DEBUG) &&
>>>>>> + !intel_display_power_is_enabled(dev_priv,
>>>>>> + POWER_DOMAIN_PIPE(pipe)));
>>>>> Uses a mutex. And having a power well enabled doesn't mean much. It
>>>>> doesn't guarantee that vblanks work.
>>>> Impasse. :|
>>>>
>>>> There should be no point in an explicit assert_rpm_wakeref here as the
>>>> register access should catch an error there. Is there no safe way we can
>>>> assert the current state of the CRTC is correct for enabling vblanks?
>>> crtc->active might be the closest thing, if we just ignore any locking.
>>> Though it looks like that has gone a bit mad these days, what with being
>>> set from the .crtc_enable() hooks but getting cleared outside the
>>> .crtc_disable() hooks.
>>>
>> I'm trying to kill crtc->active.
> Because it's evil? I still don't see much problem in having a thing to
> track the state of each pipe fairly accurately.
>
>> Maybe you'd want to use dev_priv->active_crtcs, but that won't save you if you enable interrupts in between atomic commit and .crtc_disable
> Nothing atomic based will work well because the state is not flipped at
> the same time as the actual hardware state changes.
>
>> Safest bet is to look at the power state I think.
> I don't know which power state you mean, but I already shot down the
> power domain thing.
>
>
I would say use assert_pipe_enabled then.