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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 13 Nov 2015, Bob Paauwe <bob.j.paauwe@intel.com> wrote:
> On Fri, 13 Nov 2015 19:29:41 +0200
> Mika Kuoppala <mika.kuoppala@linux.intel.com> 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);
>>  }
>>  
>>  struct request_boost {
>
> Reviewed-by: Bob Paauwe <bob.j.paauwe@intel.com>

Pushed to drm-intel-fixes, thanks for the patch and review.

BR,
Jani.



-- 
Jani Nikula, Intel Open Source Technology Center
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