Re: [PATCH] drm/i915: Avoid potential division-by-zero in computing CS timestamp period

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On 16/02/2020 18:17, Chris Wilson wrote:
Since we use a HW readback or estimation of the CS timestamp frequency,
sometimes it may result in 0. Avoid the division-by-zero in computing
its reciprocal, the timestamp period.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/intel_device_info.c | 18 +++++++++++-------
  1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_device_info.c b/drivers/gpu/drm/i915/intel_device_info.c
index a97437fac884..18d9de488593 100644
--- a/drivers/gpu/drm/i915/intel_device_info.c
+++ b/drivers/gpu/drm/i915/intel_device_info.c
@@ -1044,13 +1044,17 @@ void intel_device_info_runtime_init(struct drm_i915_private *dev_priv)
  	}
/* Initialize command stream timestamp frequency */
-	runtime->cs_timestamp_frequency_khz = read_timestamp_frequency(dev_priv);
-	runtime->cs_timestamp_period_ns =
-		div_u64(1e6, runtime->cs_timestamp_frequency_khz);
-	drm_dbg(&dev_priv->drm,
-		"CS timestamp wraparound in %lldms\n",
-		div_u64(mul_u32_u32(runtime->cs_timestamp_period_ns, S32_MAX),
-			USEC_PER_SEC));
+	runtime->cs_timestamp_frequency_khz =
+		read_timestamp_frequency(dev_priv);
+	if (runtime->cs_timestamp_frequency_khz) {
+		runtime->cs_timestamp_period_ns =
+			div_u64(1e6, runtime->cs_timestamp_frequency_khz);
+		drm_dbg(&dev_priv->drm,
+			"CS timestamp wraparound in %lldms\n",
+			div_u64(mul_u32_u32(runtime->cs_timestamp_period_ns,
+					    S32_MAX),
+				USEC_PER_SEC));
+	}

Arg this is used in i915-perf in at least one place as denominator too...


-Lionel

  }
void intel_driver_caps_print(const struct intel_driver_caps *caps,


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