drm/i915: Unmask user interrupts writes into HWSP on snb/ivb/vlv/hsw

An oddity occurs on Sandybridge, Ivybridge and Haswell (and presumably
Valleyview) in that for the period following the GPU restart after a
reset, there are no GT interrupts received. From Ville's notes, bit 0 in
the HWSTAM corresponds to the render interrupt, and if we unmask it we
do see immediate resumption of GT interrupt delivery (via the master irq
handler) after the reset.

v2: Limit the w/a to the render interrupt from rcs

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107500
Fixes: c5498089463b ("drm/i915: Mask everything in ring HWSTAM on gen6+ in ringbuffer mode")
References: d420a50c21ef ("drm/i915: Clean up the HWSTAM mess")
Testcase: igt/gem_eio/reset-stress
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180808105101.913-2-chris@chris-wilson.co.uk

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 8003cef767ba..d40f55a8dc34 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -387,8 +387,18 @@ static void intel_ring_setup_status_page(struct intel_engine_cs *engine)
                 mmio = RING_HWS_PGA(engine->mmio_base);
         }
 
-        if (INTEL_GEN(dev_priv) >= 6)
-                I915_WRITE(RING_HWSTAM(engine->mmio_base), 0xffffffff);
+        if (INTEL_GEN(dev_priv) >= 6) {
+                u32 mask = ~0u;
+
+                /*
+                 * Keep the render interrupt unmasked as this papers over
+                 * lost interrupts following a reset.
+                 */
+                if (engine->id == RCS)
+                        mask &= ~BIT(0);
+
+                I915_WRITE(RING_HWSTAM(engine->mmio_base), mask);
+        }
 
         I915_WRITE(mmio, engine->status_page.ggtt_offset);
         POSTING_READ(mmio);