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

[Ville Syrjälä]

On Tue, Nov 18, 2014 at 02:38:25PM +0530, Deepak S wrote:
> 
> On Tuesday 11 November 2014 02:25 AM, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at 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 at 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.

> 
> >   }
> >   
> >   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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-- 
Ville Syrjälä
Intel OTC