From 11caf5517c2c9eebd435c60e9343a3784d74e9a1 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 27 Oct 2017 10:43:11 +0100 Subject: [PATCH] drm/i915: Empty the ring before disabling Git-commit: 11caf5517c2c9eebd435c60e9343a3784d74e9a1 Patch-mainline: v4.16-rc1 References: FATE#322643 bsc#1055900 An interesting snippet from Sandybridge's prm: "Although a Ring Buffer can be enabled in the non-empty state, it must not be disabled unless it is empty. Attempting to disable a Ring Buffer in the non-empty state is UNDEFINED." Let's avoid the undefined behaviour as we disable the rings prior to reset and resume. V2: Tell HEAD to catch up to TAIL (empty ring) first, then reset both to 0 (supposedly while stopped). Signed-off-by: Chris Wilson Cc: Mika Kuoppala Reviewed-by: Mika Kuoppala Link: https://patchwork.freedesktop.org/patch/msgid/20171027094311.30380-1-chris@chris-wilson.co.uk Acked-by: Takashi Iwai --- drivers/gpu/drm/i915/intel_ringbuffer.c | 6 +++++- drivers/gpu/drm/i915/intel_uncore.c | 6 +++++- 2 files changed, 10 insertions(+), 2 deletions(-) --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -480,10 +480,14 @@ static bool stop_ring(struct intel_engin } } - I915_WRITE_CTL(engine, 0); + I915_WRITE_HEAD(engine, I915_READ_TAIL(engine)); + I915_WRITE_HEAD(engine, 0); I915_WRITE_TAIL(engine, 0); + /* The ring must be empty before it is disabled */ + I915_WRITE_CTL(engine, 0); + return (I915_READ_HEAD(engine) & HEAD_ADDR) == 0; } --- a/drivers/gpu/drm/i915/intel_uncore.c +++ b/drivers/gpu/drm/i915/intel_uncore.c @@ -1400,10 +1400,14 @@ static void gen3_stop_engine(struct inte DRM_DEBUG_DRIVER("%s: timed out on STOP_RING\n", engine->name); - I915_WRITE_FW(RING_CTL(base), 0); + I915_WRITE_FW(RING_HEAD(base), I915_READ_FW(RING_TAIL(base))); + I915_WRITE_FW(RING_HEAD(base), 0); I915_WRITE_FW(RING_TAIL(base), 0); + /* The ring must be empty before it is disabled */ + I915_WRITE_FW(RING_CTL(base), 0); + /* Check acts as a post */ if (I915_READ_FW(RING_HEAD(base)) != 0) DRM_DEBUG_DRIVER("%s: ring head not parked\n",