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

[Lionel Landwerlin]

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 at chris-wilson.co.uk>
> ---
>   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,