Re: [PATCH 2/4] drm/i915: Fix chv GPU freq<->opcode conversions

[Deepak S <deepak.s@intel.com>]

On Monday 17 November 2014 06:11 PM, Ville Syrjälä wrote:
> On Tue, Nov 18, 2014 at 05:59:07PM +0530, Deepak S wrote:
>> On Monday 17 November 2014 05:05 PM, Ville Syrjälä wrote:
>>> On Tue, Nov 18, 2014 at 02:38:25PM +0530, Deepak S wrote:
>>>> On Tuesday 11 November 2014 02:25 AM, ville.syrjala@linux.intel.com wrote:
>>>>> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>>>>
>>>>> Currently we miscalculate the GPU frequency on chv. This causes us to
>>>>> report the GPU frequency as half of what it really is. Drop the extra
>>>>> factor of 2 from the calculations to get the correct answer.
>>>>>
>>>>> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>>>> ---
>>>>>     drivers/gpu/drm/i915/intel_pm.c | 4 ++--
>>>>>     1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
>>>>> index 03fbb45..74e4293 100644
>>>>> --- a/drivers/gpu/drm/i915/intel_pm.c
>>>>> +++ b/drivers/gpu/drm/i915/intel_pm.c
>>>>> @@ -7329,7 +7329,7 @@ static int chv_gpu_freq(struct drm_i915_private *dev_priv, int val)
>>>>>     	if (div < 0)
>>>>>     		return div;
>>>>>     
>>>>> -	return DIV_ROUND_CLOSEST(czclk_freq * val, 2 * div) / 2;
>>>>> +	return DIV_ROUND_CLOSEST(czclk_freq * val, 2 * div);
>>>> I think CHV is 2 X cck, shouldn't we report the cck freq and not 2 *cck?
>>> Hmm. Once again the docs are extremely unclear. Dropping the 2x factor
>>> gives me the same numbers that the tables in the docs have. But then
>>> the spreadsheet calls it a "2x clock" in some places, which does suggest
>>> it might get further divided down by 2.
>>>
>>> Oh, now I did find a somewhat clear note in the clock HAS:
>>> "The dedicated GPLL (Graphics PLL) sends a 2GHz gfx clock to GenLC,
>>> which gets divided inside the GenLC block to derive a 1GHz Gfx fast clock."
>>>
>>> So based on that the original code does make more sense.
>>>
>> Do we need to mention in comment about 2 * GFX clock?
> Yeah, a comment would probably be a good idea. Could avoid some confusion
> in the future if someone else looks at this code.

Will you add the comment and submit a patch?

>>
>>>>>     }
>>>>>     
>>>>>     static int chv_freq_opcode(struct drm_i915_private *dev_priv, int val)
>>>>> @@ -7341,7 +7341,7 @@ static int chv_freq_opcode(struct drm_i915_private *dev_priv, int val)
>>>>>     		return mul;
>>>>>     
>>>>>     	/* CHV needs even values */
>>>>> -	return DIV_ROUND_CLOSEST(val * 2 * mul, czclk_freq) * 2;
>>>>> +	return DIV_ROUND_CLOSEST(val * mul, czclk_freq) * 2;
>>>>>     }
>>>>>     
>>>>>     int vlv_gpu_freq(struct drm_i915_private *dev_priv, int val)
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