Re: [PATCH 1/2] drm/i915: Stop overwriting RING_IMR in rcs resume

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On 18/04/2019 15:59, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2019-04-18 15:34:09)

On 18/04/2019 14:27, Chris Wilson wrote:
We store the engine->imr mask and set up the RING_IMR register on
restarting the engine. We do not then want to overwrite it with
an incomplete mask later as we may then lose interrupts!

Reported-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
   drivers/gpu/drm/i915/intel_ringbuffer.c | 3 ---
   1 file changed, 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 029fd8ec1857..00bd9eeb053d 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -873,9 +873,6 @@ static int init_render_ring(struct intel_engine_cs *engine)
       if (IS_GEN_RANGE(dev_priv, 6, 7))
               I915_WRITE(INSTPM, _MASKED_BIT_ENABLE(INSTPM_FORCE_ORDERING));
- if (INTEL_GEN(dev_priv) >= 6)
-             ENGINE_WRITE(engine, RING_IMR, ~engine->irq_keep_mask);
-
       return 0;
   }

Is it perhaps a way to enable L3_DPF on IVB and HSW when breadcrumbs are
off (no one listening)? Mind you, the same should be done in this case
under execlists for ctx switch irq. I just can't find the code there
which unmasks it unless a single engine->irq_enable/irq_disable cycle is
guaranteed on load indirectly. Is there a request_wait or wait_for_idle
hidden somewhere during init? Or I missed the ball completely?

See intel_engine_reset_breadcrumbs(), we always re-emit the breadcrumb
setup (IMR) for either the disabled or enabled state. That should make
sure engine->irq_keep_mask is applied.

Ah.. thanks! Although it is a bit conceptually wrong that breadcrumbs have to do the basic/unrelated engine setup. As such the legacy submission indeed looks more correct, but still wrong that engine reset can turn off user interrupts. Blah.. another pedestrian task for a rainy day.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko
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