linux-kernel - [PATCH 3.16 02/99] drm/i915/ringbuffer: Delay after EMIT

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Message-ID: <lsq.1554212307.213091977@decadent.org.uk>
Date:   Tue, 02 Apr 2019 14:38:27 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Chris Wilson" <chris@...is-wilson.co.uk>,
        "Ville Syrjälä" <ville.syrjala@...ux.intel.com>
Subject: [PATCH 3.16 02/99] drm/i915/ringbuffer: Delay after
 EMIT_INVALIDATE for gen4/gen5

3.16.65-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Wilson <chris@...is-wilson.co.uk>

commit 55f99bf2a9c331838c981694bc872cd1ec4070b2 upstream.

Exercising the gpu reloc path strenuously revealed an issue where the
updated relocations (from MI_STORE_DWORD_IMM) were not being observed
upon execution. After some experiments with adding pipecontrols (a lot
of pipecontrols (32) as gen4/5 do not have a bit to wait on earlier pipe
controls or even the current on), it was discovered that we merely
needed to delay the EMIT_INVALIDATE by several flushes. It is important
to note that it is the EMIT_INVALIDATE as opposed to the EMIT_FLUSH that
needs the delay as opposed to what one might first expect -- that the
delay is required for the TLB invalidation to take effect (one presumes
to purge any CS buffers) as opposed to a delay after flushing to ensure
the writes have landed before triggering invalidation.

Testcase: igt/gem_tiled_fence_blits
Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181105094305.5767-1-chris@chris-wilson.co.uk
[bwh: Backported to 3.16:
 - Use intel_ring_emit() instead of assignments
 - Use ring->scratch.gtt_offset instead of i915_ggtt_offset()
 - Use (invalidate_domains & I915_GEM_DOMAIN_INSTRUCTION) instead of
   (mode & EMIT_INVALIDATE)
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 38 +++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -103,6 +103,7 @@ gen4_render_ring_flush(struct intel_engi
 	struct drm_device *dev = ring->dev;
 	u32 cmd;
 	int ret;
+	int i;
 
 	/*
 	 * read/write caches:
@@ -142,12 +143,47 @@ gen4_render_ring_flush(struct intel_engi
 	    (IS_G4X(dev) || IS_GEN5(dev)))
 		cmd |= MI_INVALIDATE_ISP;
 
-	ret = intel_ring_begin(ring, 2);
+	i = 2;
+	if (invalidate_domains & I915_GEM_DOMAIN_INSTRUCTION)
+		i += 20;
+
+	ret = intel_ring_begin(ring, i);
 	if (ret)
 		return ret;
 
 	intel_ring_emit(ring, cmd);
-	intel_ring_emit(ring, MI_NOOP);
+
+	/*
+	 * A random delay to let the CS invalidate take effect? Without this
+	 * delay, the GPU relocation path fails as the CS does not see
+	 * the updated contents. Just as important, if we apply the flushes
+	 * to the EMIT_FLUSH branch (i.e. immediately after the relocation
+	 * write and before the invalidate on the next batch), the relocations
+	 * still fail. This implies that is a delay following invalidation
+	 * that is required to reset the caches as opposed to a delay to
+	 * ensure the memory is written.
+	 */
+	if (invalidate_domains & I915_GEM_DOMAIN_INSTRUCTION) {
+		intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) |
+				PIPE_CONTROL_QW_WRITE);
+		intel_ring_emit(ring, ring->scratch.gtt_offset |
+				PIPE_CONTROL_GLOBAL_GTT);
+		intel_ring_emit(ring, 0);
+		intel_ring_emit(ring, 0);
+
+		for (i = 0; i < 12; i++)
+			intel_ring_emit(ring, MI_FLUSH);
+
+		intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) |
+				PIPE_CONTROL_QW_WRITE);
+		intel_ring_emit(ring, ring->scratch.gtt_offset |
+				PIPE_CONTROL_GLOBAL_GTT);
+		intel_ring_emit(ring, 0);
+		intel_ring_emit(ring, 0);
+	}
+
+	intel_ring_emit(ring, cmd);
+
 	intel_ring_advance(ring);
 
 	return 0;