Re: [PATCH 3/3] drm/i915: go back to switch for VLV mem freq detection

[Ben Widawsky <ben@bwidawsk.net>]

On Wed, May 01, 2013 at 06:26:28PM -0700, Ben Widawsky wrote:
> On Wed, May 01, 2013 at 04:09:22PM -0700, Jesse Barnes wrote:
> > We need to catch the invalid case and override it.
> > 
> > Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> > ---
> >  drivers/gpu/drm/i915/intel_pm.c |   16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> > index 0f4b46e..0a3b0b3 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -2902,7 +2902,21 @@ static void valleyview_enable_rps(struct drm_device *dev)
> >  		   GEN7_RC_CTL_TO_MODE);
> >  
> >  	valleyview_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS, &val);
> > -	dev_priv->mem_freq = 800 + (266 * (val >> 6) & 3);
> > +	switch ((val >> 6) & 3) {
> > +	case 0:
> > +		dev_priv->mem_freq = 800;
> > +		break;
> > +	case 1:
> > +		dev_priv->mem_freq = 1066;
> > +		break;
> > +	case 2:
> > +		dev_priv->mem_freq = 1333;
> > +		break;
> > +	case 3:
> > +		DRM_ERROR("invalid mem freq, assuming 800MHz\n");
> > +		dev_priv->mem_freq = 800;
> > +		break;
> > +	}
> >  	DRM_DEBUG_DRIVER("DDR speed: %d MHz", dev_priv->mem_freq);
> >  
> >  	DRM_DEBUG_DRIVER("GPLL enabled? %s\n", val & 0x10 ? "yes" : "no");
> 
> 
> I guess it doesn't handle the last case, but:
> dev_priv->mem_freq = 800 + (266 * (val))) + val/2
> 

conveniently, I've given you the reason not to use this one... error
prone. It's missing a:
val = (val >> 6) & 3
before the math.

> or
> 
> u32 freqs[] = {800,1066,1333,800};
> dev_priv->mem_freq = freqs[(val >> 6) & 3];
> 
> Are two ways I would have used before making a switch block :P
> 
> Just a thought, but perhaps we don't want to enable RPS if we can't
> reliably figure out the memory freq. (case 3)
> 
> Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
> 
> -- 
> Ben Widawsky, Intel Open Source Technology Center
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-- 
Ben Widawsky, Intel Open Source Technology Center