From 11caf5517c2c9eebd435c60e9343a3784d74e9a1 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
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 <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171027094311.30380-1-chris@chris-wilson.co.uk
Acked-by: Takashi Iwai <tiwai@suse.de>
---
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",