linux-kernel - [PATCH 2/3] drm/msm: Fix races managing the OOB state for timestamp vs timestamps.

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Date:   Wed, 27 Jan 2021 15:39:45 -0800
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>,
        Jordan Crouse <jcrouse@...eaurora.org>
Cc:     linux-kernel@...r.kernel.org, Eric Anholt <eric@...olt.net>,
        stable@...r.kernel.org
Subject: [PATCH 2/3] drm/msm: Fix races managing the OOB state for timestamp vs timestamps.

Now that we're not racing with GPU setup, also fix races of timestamps
against other timestamps.  In CI, we were seeing this path trigger
timeouts on setting the GMU bit, especially on the first set of tests
right after boot (it's probably easier to lose the race than one might
think, given that we start many tests in parallel, and waiting for NFS
to page in code probably means that lots of tests hit the same point
of screen init at the same time).

Signed-off-by: Eric Anholt <eric@...olt.net>
Cc: stable@...r.kernel.org # v5.9
---
 drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
index 7424a70b9d35..e8f0b5325a7f 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
+++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
@@ -1175,6 +1175,9 @@ static int a6xx_get_timestamp(struct msm_gpu *gpu, uint64_t *value)
 {
 	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
 	struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
+	static DEFINE_MUTEX(perfcounter_oob);
+
+	mutex_lock(&perfcounter_oob);
 
 	/* Force the GPU power on so we can read this register */
 	a6xx_gmu_set_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
@@ -1183,6 +1186,7 @@ static int a6xx_get_timestamp(struct msm_gpu *gpu, uint64_t *value)
 		REG_A6XX_RBBM_PERFCTR_CP_0_HI);
 
 	a6xx_gmu_clear_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
+	mutex_unlock(&perfcounter_oob);
 	return 0;
 }
 
-- 
2.30.0