Re: [PATCH] drm/i915: Fix GT frequency rounding

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Fix GT frequency rounding
Date: Fri, 13 Nov 2015 19:47:25 +0200	[thread overview]
Message-ID: <20151113174725.GD4437@intel.com> (raw)
In-Reply-To: <1447435781-23416-1-git-send-email-mika.kuoppala@intel.com>

On Fri, Nov 13, 2015 at 07:29:41PM +0200, Mika Kuoppala wrote:
> When we set and later readback a frequency value through
> sysfs interface, igt/pm_rpm assumes that we get same value back
> if it matches hw granularity.
> 
> On bxt we have found out that this is not always the case.
> Currently frequency - hw ratio - frequency conversions round down,
> with few exceptions on platforms that have more specific conversions.
> On bxt the supported range can be for example from 100Mhz to 650Mhz.
> Midpoint is then calculated by test to be 375 which pm_rps uses to find a
> closest hw supported frequency. That is 366 (ratio 22),
> which it then writes back. But as the rounding down kicks in,
> driver actually sets 350 instead of 366, as 366 is 2/3 below 22 * 50/3.
> 
> Fix this by rounding to closest instead of rounding down in
> freq-ratio-freq conversions.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92768
> Testcase: igt/pm_rps/basic-api
> Tested-by: Bob Paauwe <bob.j.paauwe@intel.com>
> Cc: Bob Paauwe <bob.j.paauwe@intel.com>
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 647c0ff..740623f 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -7139,7 +7139,8 @@ static int chv_freq_opcode(struct drm_i915_private *dev_priv, int val)
>  int intel_gpu_freq(struct drm_i915_private *dev_priv, int val)
>  {
>  	if (IS_GEN9(dev_priv->dev))
> -		return (val * GT_FREQUENCY_MULTIPLIER) / GEN9_FREQ_SCALER;
> +		return DIV_ROUND_CLOSEST(val * GT_FREQUENCY_MULTIPLIER,
> +					 GEN9_FREQ_SCALER);
>  	else if (IS_CHERRYVIEW(dev_priv->dev))
>  		return chv_gpu_freq(dev_priv, val);
>  	else if (IS_VALLEYVIEW(dev_priv->dev))
> @@ -7151,13 +7152,14 @@ int intel_gpu_freq(struct drm_i915_private *dev_priv, int val)
>  int intel_freq_opcode(struct drm_i915_private *dev_priv, int val)
>  {
>  	if (IS_GEN9(dev_priv->dev))
> -		return (val * GEN9_FREQ_SCALER) / GT_FREQUENCY_MULTIPLIER;
> +		return DIV_ROUND_CLOSEST(val * GEN9_FREQ_SCALER,
> +					 GT_FREQUENCY_MULTIPLIER);
>  	else if (IS_CHERRYVIEW(dev_priv->dev))
>  		return chv_freq_opcode(dev_priv, val);
>  	else if (IS_VALLEYVIEW(dev_priv->dev))
>  		return byt_freq_opcode(dev_priv, val);
>  	else
> -		return val / GT_FREQUENCY_MULTIPLIER;
> +		return DIV_ROUND_CLOSEST(val, GT_FREQUENCY_MULTIPLIER);

lgtm

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  }
>  
>  struct request_boost {
> -- 
> 2.5.0
> 
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-- 
Ville Syrjälä
Intel OTC
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