linux-kernel - [PATCH v2 1/4] drm/msm/a5xx: disable preemption in submits by default

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Message-ID: <20240901135419.1075412-2-vladimir.lypak@gmail.com>
Date: Sun,  1 Sep 2024 13:54:00 +0000
From: Vladimir Lypak <vladimir.lypak@...il.com>
To: Vladimir Lypak <vladimir.lypak@...il.com>
Cc: Rob Clark <robdclark@...il.com>,
	Sean Paul <sean@...rly.run>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Abhinav Kumar <quic_abhinavk@...cinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Jordan Crouse <jordan@...micpenguin.net>,
	linux-arm-msm@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	freedreno@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/4] drm/msm/a5xx: disable preemption in submits by default

Fine grain preemption (switching from/to points within submits)
requires extra handling in command stream of those submits, especially
when rendering with tiling (using GMEM). However this handling is
missing at this point in mesa (and always was). For this reason we get
random GPU faults and hangs if more than one priority level is used
because local preemption is enabled prior to executing command stream
from submit.
With that said it was ahead of time to enable local preemption by
default considering the fact that even on downstream kernel it is only
enabled if requested via UAPI.

Fixes: a7a4c19c36de ("drm/msm/a5xx: fix setting of the CP_PREEMPT_ENABLE_LOCAL register")
Signed-off-by: Vladimir Lypak <vladimir.lypak@...il.com>
---
 drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
index c0b5373e90d7..6c80d3003966 100644
--- a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
+++ b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
@@ -150,9 +150,13 @@ static void a5xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
 	OUT_PKT7(ring, CP_SET_PROTECTED_MODE, 1);
 	OUT_RING(ring, 1);
 
-	/* Enable local preemption for finegrain preemption */
+	/*
+	 * Disable local preemption by default because it requires
+	 * user-space to be aware of it and provide additional handling
+	 * to restore rendering state or do various flushes on switch.
+	 */
 	OUT_PKT7(ring, CP_PREEMPT_ENABLE_LOCAL, 1);
-	OUT_RING(ring, 0x1);
+	OUT_RING(ring, 0x0);
 
 	/* Allow CP_CONTEXT_SWITCH_YIELD packets in the IB2 */
 	OUT_PKT7(ring, CP_YIELD_ENABLE, 1);
-- 
2.46.0